TN70S 
03 


IRON   AND   STEEL 


IRON  AND  STEEL 

A  TREATISE  ON  THE  SMELTING,  REFINING,  AND 
MECHANICAL  PROCESSES  OF  THE  IRON  AND 
STEEL  INDUSTRY,  INCLUDING  THE  CHEMICAL 
AND  PHYSICAL  CHARACTERISTICS  OF  WROUGHT 
IRON,  CARBON,  HIGH-SPEED  AND  ALLOY  STEELS, 
CAST  IRON,  AND  STEEL  CASTINGS,  AND  THE 
APPLICATION  OF  THESE  MATERIALS  IN  MA- 
CHINE AND  TOOL  CONSTRUCTION 


BY 

ERIK   OBERG 

EDITOR  OF  MACHINERY 

EDITOR  OP  MACHINERY'S  HANDBOOK  AND  MACHINERY'S 

ENCYCLOPEDIA.    AUTHOR  OF   '  HANDBOOK  OF 

SMALL  TOOLS,"  ETC. 

AND 

FRANKLIN    D.   JONES 

ASSOCIATE  EDITOR  OF  MACHINERY 

AUTHOR  OF  "TURNING  AND  BORING,"   "PLANING  AND  MILLING," 

"MECHANISMS  AND  MECHANICAL  MOVEMENTS," 

"THREAD -CUTTING  METHODS,"  ETC. 

IN  COLLABORATION  WITH  PROMINENT  METALLURGISTS 
AND  STEEL-MAKERS 


FIRST  EDITION 
SECOND    PRINTING 


NEW  YORK 

THE   INDUSTRIAL    PRESS 

LONDON:    THE   MACHINERY   PUBLISHING  CO.,  LTD. 

1920 


COPYRIGHT,  1918, 

BY 

THE  INDUSTRIAL  PRESS 
NEW  YORK 


COMPOSITION  AND  ELECTROTYPING  BY  F.  H.  GILSON  COMPANY,  BOSTON,  U.  S.  A. 


PREFACE 


As  the  transformation  of  crude  iron  ore  into  various  classes  or 
grades  of  iron  and  steel  requires  the  knowledge  of  the  chemist, 
the  experience  and  skill  of  the  iron-  and  steel-maker,  and  a  great 
variety  of  mechanical  and  electrical  equipment  for  the  various 
processes,  many  volumes  of  this  size  would  be  needed  to  cover 
every  phase  of  iron  and  steel  manufacture.  No  attempt,  there- 
fore, has  been  made  to  prepare  a  complete  treatise  for  metal- 
lurgists and  other  specialists  connected  with  the  manufacture 
of  iron  and  steel,  but  rather  a  text-book  suitable  for  students  in 
technical  schools  and  those  in  the  machine  building  and  mechan- 
ical engineering  fields  who  want  a  broad  general  survey  of  the 
iron  and  steel  industry,  with  definite  practical  information  per- 
taining to  the  various  commercial  forms  and  grades  of  iron  and 
steel  products,  and  the  particular  class  of  service  for  which  the 
different  grades  are  applicable. 

Steel  having  almost  any  desired  physical  characteristics  may 
now  be  obtained  and  great  progress  has  also  been  made  in  the 
making  of  iron  and  steel  castings,  but  these  products  of  the 
steel-maker  and  metallurgist  have  not  always  been  used  to 
advantage  by  the  designer  and  manufacturer.  Expensive  ma- 
terials are  often  employed  where  cheaper  grades  would  meet 
every  requirement,  or  this  order  may  be  reversed,  low-grade 
products  being  used  where  the  best  and  most  costly  materials 
would  ultimately  prove  economical.  Because  of  these  facts, 
the  relation  between  the  different  grades  and  qualities  of  iron 
and  steel  and  the  particular  use  for  which  each  kind  is  adapted 
are  emphasized  in  this  book. 

The  various  refining  and  mechanical  processes  of  the  iron  and 
steel  industry  have  been  described  quite  completely  in  some 
instances  because  of  the  close  relationship  between  the  manu- 


vi  PREFACE 

facturing  method  and  the  characteristics  of  the  product.  The 
chapters  dealing  with  iron  ore  and  the  making  of  pig  iron  are 
followed  by  others  on  wrought  iron,  structural  steels,  tool  steels, 
alloy  steels,  cast  iron,  steel  castings,  and  the  methods  of  rolling 
and  drawing  bars,  flat  plates,  shafting,  and  wire.  It  is  believed 
that  the  treatment  of  these  different  subjects  will  be  appreciated 
by  designers  of  machinery  or  tools  as  well  as  manufacturers  and 
workers  in  metal  who  realize  that  a  knowledge  of  the  materials 
which  are  so  closely  related  to  their  work  is  of  great  value  if  not 
absolutely  essential,  especially  at  the  present  time  when  so  many 
different  grades  of  iron  and  steel  may  be  obtained  from  the  steel 
mill  and  foundry. 

THE  AUTHORS. 

NEW  YORK,  October, 


SELF-  EXAMINATION 

Sheet  No.  16 


For  Machinery's  Book 

"IRON  AND  STEEL" 

These  self-examination  sheets  are  designed  to 
assist  buyers  of  MACHINERY'S  books  in  testing 
their  knowledge  of  each  subject  studied.  The 
whole  idea  is  to  help  the  reader  get  the  utmost 
possible  value  out  of  each  book. 

First,  study  this  book  thoroughly.  Then  try  to 
answer  to  your  own  satisfaction  the  list  of 
questions  beginning  on  the  next  page.  If  you 
cannot  answer  the  questions  satisfactorily  to 
yourself,  write  to  us  giving  both  Examination 
Sheet  number  and  question  number,  and  we 
will  tell  you  what  parts  of  the  book  to  study. 


Home  Study  Self-examination  Sheet  No.  16 
TEST  QUESTIONS  FOR 

"IRON  AND  STEEL" 


1.  Name  the  fuels  ordinarily  used  in  blast  furnaces. 

2.  How  is  pig  iron  classified  and  graded? 

3.  What  are  the  general  characteristics  of  wrought  iron, 
and   in  what  respects   does   it  differ  from  low-carbon 
steel? 

4.  In  what  way  does  carbon  affect  the  physical  properties 
of  steel? 

5.  What  is  crucible  steel? 

6.  Explain  the  general  principle  (1)  of  the  Bessemer  pro- 
cess;   (2)   of  the  open-hearth  process. 

7.  What  process  is  employed  for  making  most  of  the  struc- 
tural steel  used? 

8.  What  are  the  advantages  of  the  electric  process  of  steel 
making? 

9.  How  is  cold-drawn  shafting  produced? 

10.  Why  is   sheet   stock  often   subjected  to   a   cold-rolling 
process  ? 

11.  How  is  wire  produced? 

12.  About  how  much  carbon  does  machine  steel  contain? 

13.  Explain  the   difference  between  alloy  steels   and  plain 
carbon  steels. 


Home  Study  Self-examination  Sheet  No.  16 

14.  Why  are  high-speed  steels  so  named,  and  what  are  their 
chief  characteristics? 

15.  How  much  carbon  does  spring  steel  ordinarily  contain? 

16.  What  are  "natural  alloy4  steels"? 

17.  What  are  semi-steel  castings  and  why  are  they  used? 

18.  How  should  steel  castings  be  annealed? 


Can  You  Answer  These  Questions? 

The  following  test  questions  are  for  MACHINERY'S 
book  "Heat-treatment  of  Steel" — a  companion  book 
to  "Iron  and  Steel." 

1.  How    are   the    correct   hardening   temperatures    deter- 
mined for  different  kinds  of  steel? 

2.  What  is   the   distinction  between  hardening  and  tem- 
pering? 

3.  Why  are  molten  baths  often  used  for  heating  steel  prep- 
aratory to  hardening? 

4.  Does  the  kind  of  quenching  bath  affect  the  hardness  of 
steel? 

5.  How  are  oil  baths  used  for  tempering? 

6.  Is  high-speed  steel  tempered  after  hardening? 

7.  What  causes  the  formation  of  scale  on  heated  steel? 

8.  What  is  pack-hardening? 

9.  Explain  the  general  principles  of  casehardening. 


Home  Study  Self-examination  Sheet  No.  16 

10.  Can    casehardened    parts    be    given    different   physical 
properties  by  varying  the  heat-treatment? 

11.  How     much     carbon     should     casehardened     surfaces 
contain  ? 

12.  What  methods  are  employed  for  testing  the  hardness  of 
metal? 

13.  In  what  way  is  the  hardness   of   steel   related   to  its 
strength  ? 

14.  How  can  mottled  and  colored  effects  be  obtained  when 
casehardening? 

15.  What  is  the  object  of  heat-treating  alloy  steels  of  the 
class  used  for  structural  purposes  ? 

16.  How  are  steels  annealed? 

17.  What  is  the  cause  of  most  hardening  defects? 

18.  Why  is  it  possible  to  determine,  with  a  fair  degree  of 
accuracy,  the  proper  hardening  temperature  for  tool 
steel  by  using  a  magnet  or  pocket  compass  ? 


To  answer  these  questions  requires 
a  practical  knowledge  of  steel  and 
its  heat- treatment,  which  can  be  ob- 
tained readily  from  MACHINERY'S 
books  on  these  subjects.  These 
books  are  educators. 


MACHINERY,  140-148  Lafayette  St.,  N.  Y. 

Copyright  1923,   The  Industrial  Press,   New  York  City. 


CONTENTS 


CHAPTER  I 
CLASSIFICATION  OF  IRON  AND   STEEL 

PAGES 

Review  of  Processes  —  History  of  Iron  Industry  —  Strength 
of  Iron  and  Steel 1-15 

CHAPTER  II 
IRON  ORE  AND  ITS  PREPARATION  FOR  SMELTING 

Kinds  of  Ore  —  Influence  of  Various  Elements  on  Iron  Ore 
—  Beneficiation 


CHAPTER  III 
PIG  IRON  AND  ITS  PRODUCTION 

Blast  Furnace  Operation  —  Fuels  —  Grades  of  Pig  Iron . . .     34-64 

CHAPTER  IV 
WROUGHT  IRON  AND  ITS  MANUFACTURE 

Characteristics  —  Manufacturing  Processes 65-80 

CHAPTER  V 
CLASSIFICATION  AND   CHARACTERISTICS  OF  STEEL 

Kinds    of    Steel  —  Microscopic    Examination  —  Effect    of 
Different  Elements 81-116 

CHAPTER  VI 
CRUCIBLE  STEEL 
Crucible  Process  —  Types  of  Melting  Furnaces 117-133 

CHAPTER  VII 
BESSEMER  PROCESS 

Principle  of  Process  —  Operation  of  Converters 134-151 

vii 


Vili  CONTENTS 

CHAPTER  VIII 

PAGES 

OPEN-HEARTH   STEEL 
Basic  and  Acid  Processes  —  Furnaces  Used  —  Charging     152-180 

CHAPTER  IX 
ELECTRIC   STEEL 

Types  of  Furnaces  —  Advantages  and  Application  of  Elec- 
tric Furnaces 181-203 

CHAPTER  X 

ROLLING  AND   DRAWING  BARS,   RAILS,   PLATES, 
SHAFTING,  AND  WIRE 

Rolling   Mills   and   Rolling   Processes  —  Cold   Drawing  — 
Dies  Used  for  Cold  Rolling  Sheet  Stock  —  Wire  Drawing. .     204-253 

CHAPTER  XI 
STRUCTURAL   CARBON  AND   ALLOY  STEELS 

Uses  of  Different  Carbon  and  Alloy  Steels  —  Chemical  and 
Physical  Characteristics 254-275 

CHAPTER  XII 
HIGH-SPEED   STEEL 

Origin  —  Heat-treatment  —  Production  —  Hardening    Prac- 
tice —  Influence  of  Different  Elements 276-297 

CHAPTER  XIII 
CAST  IRON 

Different  Grades  of  Cast  Iron  —  Composition  —  Strength 
—  Production 298-309 

CHAPTER  XIV 
STEEL  CASTINGS 

Strength  —  Production  —  Application  —  Use  of  the   Elec- 
tric Furnace 310-321 


IRON   AND   STEEL 


CHAPTER  I 

CLASSIFICATION   OF  IRON  AND    STEEL  AND    REVIEW    OF 
MANUFACTURING  PROCESSES 

THE  term  "  iron,"  as  used  in  the  chemical  or  scientific  sense  of 
the  word,  refers  to  the  chemical  element  iron  or  pure  iron,  which 
is  the  chief  constituent  in  all  commercial  iron  and  steel.  As 
applied  to  the  commercial  product,  however,  the  term  "iron"  is 
most  generally  used  to  indicate  wrought  iron,  as  distinguished 
from  steel  or  cast  iron.  Pure  iron  is  not  used  in  the  industries, 
but  all  the  commercial  products  containing  iron  as  the  chief 
element  —  wrought  iron,  cast  iron,  steel  castings,  Bessemer  steel, 
open-hearth  steel,  crucible  steel,  alloy  steel,  etc.,  —  contain  also 
small  percentages  of  carbon  and  a  number  of  other  elements,  the 
presence  of  which  determine  the  characteristics  of  each  class  of 
commercial  iron  and  steel.  Iron  is  found  in  nature  in  the  form 
of  iron  ore,  and  all  the  irons  and  steels  used  in  the  industries  are 
produced  from  iron  ore  by  a  number  of  different  processes,  each 
suited  to  the  ultimate  product  desired. 

Pure  Iron.  —  Iron  is  one  of  the  most  abundant  elements  in  * 
nature,  and  is  estimated  to  constitute  by  weight  4.3  per  cent  of 
the  earth's  crust.  It  excels  all  other  metals  in  magnetic  prop- 
erties, and  when  small  percentages  of  other  elements  are  added 
to  it,  it  excels  in  strength  and  in  the  property  of  attaining  great 
hardness  or  ductility  by  suitable  heat-treatment.  It  can  also 
be  easily  welded  and  forged.  Because  of  its  abundant  supply 
and  its  strength,  ductility,  and  malleability,  iron  is  the  most 
important  of  the  metallic  elements,  and  present  civilization 
would  be  impossible  without  it.  Over  seventy-five  million  tons 
are  now  used  annually  for  rails,  wire,  machinery,  structural 
materials,  cutting  tools,  etc. 


2  IRON  AND  STEEL 

Pure  iron  is  silvery  white,  tenacious,  malleable,  ductile,  and 
has  a  high  melting  point.  The  chemical  symbol  of  iron  is  Fe, 
its  atomic  weight  is  55.84,  and  its  specific  gravity,  7.84,  giving  a 
weight  per  cubic  inch  of  0.283  pound.  Its  linear  expansion  per 
unit  length  in  degrees  F.  is  0.0000065,  and  its  average  specific 
heat  for  temperatures  between  60  and  212  degrees  F.,  o.n; 
this  value  of  the  specific  heat  increases  with  the  temperature,  up 
to  about  1550  degrees  F.,  and  then  diminishes.  The  melting 
point  of  pure  iron  is  given  by  the  Bureau  of  Standards  as  1520 
degrees  C.  (2768  degrees  F.),  but  as  temperatures  above  1000 
degrees  C.  are  difficult  to  measure  exactly,  it  should  be  under- 
stood that  the  figures  given  are  not  known  exactly  to  within 
more  than  five  or  ten  degrees.  Commercial  iron  or  steel  which 
contains  carbon,  silicon,  phosphorus,  sulphur,  etc.,  has  a  lower 
melting  point,  carbon  especially  having  the  property  of  reducing 
the  melting  point  as  well  as  the  ductility  of  the  metal,  but  in- 
creasing the  hardness.  The  amount  of  the  other  elements  pres- 
ent affects  the  properties  of  the  iron  and  steel  for  different  pur- 
poses. Variations  in  the  mechanical  working  and  heat- treat- 
ment of  iron  and  steel  also  produce  corresponding  variations  in 
the  properties  of  the  commercial  metal.  Pure  iron  is  attracted 
by  a  magnet,  but  does  not  retain  magnetization.  When  ex- 
posed to  the  atmosphere,  it  is  rapidly  oxidized  or  corroded,  the 
corrosion  generally  being  termed  "  rust." 

Commercial  Iron  and  Steel.  —  As  mentioned,  all  commercial 
iron  or  steel  contains  iron  as  the  chief  constituent,  but  the  per- 
centages of  carbon  and  other  elements  that  iron  or  steel  con- 
tains and  the  methods  by  which  they  are  produced,  as  well  as 
the  processes  to  which  they  may  be  subjected,  so  change  the 
characteristic  properties  that  there  are  many  distinct  forms  of 
iron  and  steel,  some  of  which  have  properties  so  different  as  to 
appear  like  different  metals.  The  main  classes  are  pig  iron, 
wrought  iron,  Bessemer  steel,  open-hearth  steel,  crucible  steel, 
alloy  steel,  cast  iron,  and  steel  castings.  Pig  iron  is  the  product 
into  which  the  iron  ore  is  first  converted  in  a  blast  furnace. 
From  pig  iron,  all  commercial  irons  and  steels  are  made. 
Wrought  iron  is  produced  by  what  is  known  as  the  "  puddling" 


CLASSIFICATION  3 

process.  It  contains  a  lower  percentage  of  carbon  than  other 
forms  of  iron  and  steel,  and  is  fibrous,  ductile,  and  malleable. 
When  heated,  it  can  be  formed  and  shaped  by  forging,  with 
great  ease,  and  can  readily  be  welded;  hence  it  is  the  best 
known  material  for  making  chain,  crane  hooks,  etc.  Bessemer 
steel  is  made  from  pig  iron  in  a  Bessemer  converter;  hence  its 
name.  Open-hearth  steel  is  produced  from  pig  iron  in  a  so-called 
"  regenerative "  furnace,  the  hearth  of  which  is  exposed  to  the 
action  of  the  flame.  Steel  made  by  both  the  Bessemer  process 
and  the  open-hearth  process  is  used  for  rails,  and  also  for  struc- 
tural iron  shapes.  It  is  also  often  known  as  "mild  steel"  or 
"  machine  steel."  Crucible  steel  is  made  from  high-grade  wrought 
iron,  by  adding  carbon  to  it,  by  melting  the  wrought  iron  in 
crucibles  containing  the  proper  amount  of  powdered  charcoal. 
Crucible  steel  generally  contains  a  larger  percentage  of  carbon 
than  any  of  the  other  steels,  and  is  frequently  termed  "  tool 
steel/'  because  it  is  mainly  used  for  cutting  tools.  Alloy  steels 
may  be  made  by  any  of  the  processes  mentioned,  by  adding 
other  metals,  such  as  chromium,  nickel,  tungsten,  etc.  Cast 
iron  is  generally  produced  from  pig  iron  in  what  is  known  as  a 
"cupola"  furnace.  It  contains  a  larger  proportion  of  carbon 
than  any  of  the  other  forms  of  iron  or  steel,  and  is  easily  cast  in 
molds,  but  is  neither  ductile  nor  malleable.  Steel  castings  are 
made  from  steel,  generally  melted  in  an  open-hearth  furnace, 
electric  furnace,  or  a  small  Bessemer  converter;  crucible  steel 
castings  are  also  made. 

At  one  time,  there  was  quite  a  distinct  line  of  demarkation 
between  wrought  iron  and  steel,  but  now  these  are  distinguished 
mainly  by  their  physical  characteristics,  wrought  iron  having  a 
fibrous  structure,  while  steel  has  more  of  a  grain  or  crystalline 
structure. 

Classification  of  Iron  and  Steel.  —  At  the  Brussels  Congress 
of  the  International  Association  for  Testing  Materials,  held  in 
September,  1906,  the  following  definitions  of  the  most  impor- 
tant forms  of  iron  and  steel  were  adopted: 

Alloy  Cast  Iron.  —  Iron  which  owes  its  properties  chiefly  to 
the  presence  of  an  element  other  than  carbon. 


4  IRON  AND   STEEL 

Alloy  Steel.  —  Steel  which  owes  its  properties  chiefly  to  the 
presence  of  an  element  other  than  carbon. 

Basic  Pig  Iron.  —  Pig  iron  containing  so  little  silicon  and 
sulphur  that  it  is  suited  for  easy  conversion  into  steel  by  the 
basic  open-hearth  process  (restricted  to  pig  iron  containing  not 
more  than  i  per  cent  of  silicon). 

Bessemer  Pig  Iron.  —  Iron  which  contains  so  little  phosphorus 
and  sulphur  that  it  can  be  used  for  conversion  into  steel  by  the 
original  or  acid  Bessemer  process  (res  trie  ted  to  pig  iron  con- 
taining not  more  than  o.io  per  cent  of  phosphorus). 

Bessemer  Steel.  —  Steel  made  by  the  Bessemer  process,  irre- 
spective of  carbon  content. 

Blister  Steel.  —  Steel  made  by  carburizing  wrought  iron  by 
heating  it  in  contact  with  carbonaceous  matter.  (Also  known 
as  "converted  steel.") 

Cast  Iron.  —  Iron  containing  so  much  carbon  or  its  equivalent 
that  it  is  not  malleable  at  any  temperature.  The  line  between 
cast  iron  and  steel  is  generally  drawn  at  2.20  per  cent  carbon. 

Cast  Steel.  —  The  same  as  crucible  steel;  obsolete,  and  to  be 
avoided  because  confusing. 

Charcoal  Hearth  Cast  Iron.  —  Cast  iron  which  has  had  its 
silicon  and  usually  its  phosphorus  removed  in  the  charcoal 
hearth,  but  still  contains  so  much  carbon  as  to  be  distinctly 
cast  iron. 

Converted  Steel.  —  The  same  as  blister  steel. 

Crucible  Steel.  —  Steel  made  by  the  crucible  process,  irrespec- 
tive of  carbon  content. 

Gray  Pig  Iron  and  Gray  Cast  Iron.  —  Pig  iron  and  cast  iron 
in  the  fracture  of  which  the  iron  itself  is  nearly,  or  quite,  con- 
cealed by  graphite,  so  that  the  fracture  has  the  gray  color  of 
graphite. 

Malleable  Castings.  —  Castings  made  from  iron  which,  when 
first  made,  is  in  the  condition  of  cast  iron,  and  is  made  malleable 
by  subsequent  treatment  without  fusion. 

Malleable  Iron.  —  The  same  as  wrought  iron. 

Malleable  Pig  Iron.  —  An  American  trade  name  for  the  pig 
iron  suitable  for  converting  into  malleable  castings  through  the 


CLASSIFICATION  5 

process  of  melting,  treating  when  molten,  casting  in  a  brittle 
state,  and  then  making  malleable  without  remelting. 

Open-hearth  Steel.  —  Steel  made  by  the  open-hearth  process, 
irrespective  of  carbon  content. 

Pig  Iron.  —  Cast  iron  which  has  been  cast  into  pigs  direct 
from  the  blast  furnace. 

Puddled  Iron.  —  Wrought  iron  made  by  the  puddling  process. 

Puddled  Steel.  —  Steel  made  by  the  puddling  process,  and 
necessarily  slag-bearing. 

Refined  Cast  Iron.  —  Cast  iron  which  has  had  most  of  its 
silicon  removed  in  the  refinery  furnace,  but  still  contains  so 
much  carbon  as  to  be  distinctly  cast  iron. 

Shear  Steel.  —  Steel,  usually  in  the  form  of  bars,  made  from 
blister  steel  by  shearing  it  into  short  lengths,  piling,  and  welding 
these  by  rolling  or  hammering  them  at  a  welding  heat.  If  this 
process  of  shearing,  piling,  etc.,  is  repeated,  the  product  is 
called  " double  shear  steel." 

Steel.  —  Metal  which  is  malleable  at  least  in  some  one  range 
of  temperature,  and,  in  addition,  is  either  (a)  cast  into  an  ini- 
tially malleable  mass;  or  (b)  is  capable  of  hardening  greatly  by 
sudden  cooling ;  or  (c)  is  both  so  cast  and  so  capable  of  hardening. 

Steel  Castings.  —  Unforged  and  unrolled  castings  made  of 
Bessemer,  open-hearth,  crucible,  or  any  other  steel. 

Washed  Metal.  —  Cast  iron  from  which  most  of  the  silicon 
and  phosphor  have  been  removed  by  the  Bell-Krupp  process, 
without  removing  much  of  the  carbon,  so  that  it  still  contains 
enough  carbon  to  be  cast  iron. 

Weld  Iron.  —  The  same  as  wrought  iron;  obsolete  and  need- 
less. 

White  Pig  Iron  and  White  Cast  Iron.  —  Pig  iron  and  cast  iron 
in  the  fracture  of  which  little  or  no  graphite  is  visible,  so  that 
their  fracture  is  silvery  and  white. 

Wrought  Iron.  —  Slag-bearing  malleable  iron  which  does  no', 
harden  materially  when  suddenly  cooled. 

Outline  of  Iron-  and  Steel-making  Processes.  —  In  outlining 
the  different  processes  for  the  production  of  iron  and  steel,  the 
method  of  obtaining  pig  iron  from  the  iron  ore  is  the  basic 


IRON  AND  STEEL 


MANUFACTURING    PROCESSES  7 

process.  When  iron  ore,  which  is  an  oxide  of  iron  containing, 
ordinarily,  from  35  to  70  per  cent  of  pure  iron,  is  placed  in  a 
blast  furnace,  together  with  limestone,  which  is  used  as  a  flux, 
and  melted  with  either  coke,  anthracite  coal,  or  charcoal  used 
as  a  fuel,  the  metal  obtained  is  commercially  known  as  "pig 
iron."  The  flux  serves  the  purpose  of  uniting  with  the  impuri- 
ties of  the  ore  and  forms  cinder  or  slag,  which  is  withdrawn 
from  the  furnace  at  intervals.  The  fuel  furnishes  the  required 
heat  for  melting  the  ore.  As  the  impurities  are  removed  from 
the  ore  in  the  form  of  slag,  metallic  iron  is  formed,  which  is 
drawn  from  the  furnace  and  cast  into  small  bars,  known  as 
"pigs,"  unless  it  is  to  be  converted  into  steel  by  the  Bessemer 
process  without  being  cast  into  "pigs,"  which  is  a  modern 
method.  (The  accompanying  illustration  shows  an  ore  steamer, 
the  unloading  equipment,  and,  in  the  background,  a  blast  fur- 
nace.) Pig  iron  contains  about  93  per  cent  of  pure  iron,  from 
3  to  5  per  cent  of  carbon,  and  some  silicon,  phosphorus,  and 
sulphur.  Pig  iron  is  used  in  foundries  for  making  iron  castings, 
and  in  connection  with  the  puddling,  Bessemer,  and  open- 
hearth  processes  for  the  production  of  wrought  iron,  Bessemer 
steel,  and  open-hearth  steel,  respectively. 

Wrought  Iron.  —  In  the  making  of  wrought  iron,  pig  iron  is 
melted  in  what  is  known  as  a  "puddling"  furnace,  in  which 
most  of  the  silicon,  carbon,  and  phosphorus  in  the  pig  iron  are 
separated  from  it,  forming  puddle  cinder.  The  temperature  of 
the  puddling  furnace  is  high  enough  to  melt  pig  iron,  but  is  not 
high  enough  to  keep  wrought  iron  in  a  liquid  state,  pig  iron 
melting  at  about  2100  degrees  F.,  while  wrought  iron  melts  at 
about  2700  degrees  F.  On  account  of  this  difference  in  melting 
temperatures,  small  particles  of  iron,  when  they  have  become 
free  from  the  impurities,  will  partly  congeal,  forming  a  spongy 
mass  in  which  the  iron  is  in  a  semi-plastic  state.  This  mass  is 
divided  into  puddle  balls  or  lumps  of  about  200  pounds  each, 
which  are  formed  into  "blooms"  and  then,  while  still  hot, 
rolled  into  bars.  These  bars  are  generally  cut  up  and  again 
heated  and  rolled  one  or  more  times,  according  to  the  degree 
of  refinement  of  the  wrought  iron  required. 


8  IRON  AND   STEEL 

Bessemer  Steel.  —  Bessemer  steel  is  made  by  placing  molten 
pig  iron  in  a  large  container,  known  as  a  "  converter/'  in  which 
the  impurities  are  oxidized  and  removed  by  blowing  air  through 
the  molten  mass,  from  the  bottom  of  the  converter,  the  com- 
pressed air  having  sufficient  pressure  to  prevent  the  molten 
metal  from  entering  the  holes  or  tuyeres  through  which  it  is 
blown  into  the  converter.  Generally,  the  carbon  in  the  molten 
metal  is  almost  entirely  burned  out,  and  then  a  certain  amount 
of  spiegeleisen  or  ferromanganese,  containing  large  percentages 
of  carbon,  is  added  in  a  liquid  form  to  give  the  steel  the  proper 
amount  of  carbon  and  manganese  for  the  purpose  for  which  it 
is  intended.  The  liquid  steel  is  then  poured  into  ingot  molds, 
and  the  resulting  ingots,  while  still  hot,  are  rolled  into  blooms, 
billets,  or  rails. 

Open-hearth  Steel.  —  Open-hearth  steel  is  made  by  removing 
the  impurities  in  the  pig  iron  on  the  hearth  of  a  regenerative 
furnace,  the  hearth  being  exposed  or  open  to  the  action  of  the 
flame  from  the  fuel.  The  heat  is  produced  by  burning  gas 
from  bituminous  coal;  oil  and  natural  gas  may  also  be  used. 
To  the  charge  of  molten  metal  is  added  certain  proportions  of 
ore,  iron  scale,  or  other  oxides,  the  chemical  reaction  of  which 
keeps  the  molten  iron  in  a  state  of  agitation.  Scrap  of  wrought 
iron  or  steel  may  also  be  used,  because  the  high  temperature  in 
the  furnace  will  readily  melt  it.  Burnt  lime  is  added  to  absorb 
the  phosphorus  in  the  pig  iron,  thus  taking  it  out  of  the  metal. 

Crucible  Steel.  —  Crucible  or  tool  steel  is  made  by  adding 
carbon  to  high-grade  wrought  iron  containing  as  small  a  per- 
centage of  phosphorus  as  possible.  Small  pieces  of  wrought  iron 
are  placed  in  air-tight  crucibles  containing  the  required  amount 
of  powdered  charcoal.  This  charge  is  then  melted  in  a  furnace 
and  the  metal  cast  into  ingots,  which  are  hammered  and  rolled 
to  the  required  size.  If  the  steel  is  to  contain  chromium,  tung- 
sten, etc.,  these  ingredients  are  also  added  in  the  crucible.  The 
adding  of  carbon  to  wrought  iron,  in  order  to  convert  it  into 
tool  steel,  gives  the  latter  the  property  of  being  capable  of 
hardening;  that  is,  of  assuming  greater  hardness  if  heated  to  a 
given  temperature  and  then  quenched  in  water  or  oil. 


MANUFACTURING  PROCESSES  9 

Cast  Iron.  —  Cast  iron  is  made  from  pig  iron  by  melting  the 
pig  iron  in  a  cupola  furnace  and  adding  certain  percentages  of 
cast-iron  scrap.  Cast  iron  may  be  either  gray  or  white,  accord- 
ing to  the  form  in  which  the  carbon  in  it  is  present.  When  the 
carbon  is  in  the  " graphitic"  form,  the  fracture  is  gray  in  color, 
and,  hence,  the  iron  is  known  as  "gray  iron";  when  present  in 
the  combined  form,  the  fracture  is  mottled  or  white,  and  the 
product  is  known  as  "mottled  iron"  or  "white  iron."  Cast 
iron,  after  having  been  melted  in  the  cupola  furnace,  is  poured 
in  the  molten  state  into  molds  shaped  according  to  the  required 
size  and  form  of  the  castings  it  is  desired  to  make. 

Malleable  castings  are  made  from  white  iron  castings  by 
heating  the  latter  to  a  high  temperature  in  retorts  or  annealing 
pots,  together  with  hematite  ore.  The  oxygen  in  the  ore  ab- 
sorbs the  carbon  in  the  iron  so  that  the  surface  of  the  cast  iron 
assumes  the  nature  of  steel,  and,  hence,  is  stronger  and  tougher 
than  is  ordinary  cast  iron. 

Steel  Castings.  —  Steel  castings  are  made  from  metal  melted 
either  in  an  open-hearth  furnace,  a  Bessemer  converter,  an 
electric  furnace,  or  in  crucibles.  The  raw  materials  used  for 
steel  castings  are  pig  iron,  iron  ore,  and  steel  scrap,  the  bulk  of 
the  charge  being  scrap,  so  as  to  give  the  molten  mass  the  nature 
of  steel.  The  molten  metal  is  poured  into  molds  the  same  as  is  . 
cast  iron,  but  the  castings  are  frequently  annealed  after  having 
cooled  off  in  the  mold.  The  annealing  consists  in  placing  them 
in  furnaces  which  are  heated  to  temperatures  of  from  1200  to 
1600  degrees  F.,  in  which  they  are  kept  for  a  certain  length  of 
time,  according  to  their  size  and  the  requirements  for  which 
the  castings  are  intended.  They  are  then  permitted  to  cool 
gradually  in  the  furnaces  without  being  exposed  to  the  air. 

Brief  History  of  Iron  Industry.  —  Iron  is  thought  to  have 
been  used  in  Egypt,  Chaldea,  Assyria,  and  China  4000  years 
before  the  Christian  era,  and  to  have  been  known  in  Middle 
Europe  some  time  before  the  invasion  of  Caesar.  Homer  speaks 
of  its  use  by  the  Greeks  twelve  centuries  before  the  birth  of 
Christ,  and  his  descriptions  show  that  the  working  of  iron  must 
have  reached  a  high  state  of  development  in  his  time,  three 


10  IRON  AND  STEEL 

centuries  later.  Iron  was  known  in  Etruria  about  as  early  as 
in  Greece,  and  in  Gaul,  six  centuries  later,  but  it  was  not  known 
in  Ireland  and  Denmark  until  the  first  century  of  the  present 
era,  and  not  in  Russia  and  Siberia  until  eight  centuries  later. 

Iron  was  first  produced  in  North  America  along  the  James 
River,  Virginia,  in  1622,  and  was  made  in  Lynn,  Massachusetts, 
nine  years  later.  Colonel  Morris  built  his  "  bloomery  "  in  Mon- 
mouth  Co.,  New  Jersey,  fifty  years  later,  and  the  first  forge  in 
Pennsylvania  was  built  along  the  Schuylkill,  in  1717.  In  1750, 
New  York's  first  iron  works  was  built  at  Stirling,  where  was 
made  the  1 86-ton  chain  that  was  used  to  bar  the  Hudson  river 
in  1778.  Between  1717  and  1770,  the  industry  had  grown 
sufficiently  for  the  colonies  to  export  to  England  about  150,000 
tons  of  pig  and  bar  iron;  most  of  this  was  exported  before  1750. 

Because  of  the  ease  with  which  iron  is  extracted  from  its  ores, 
many  metallurgists  claim  that  iron  must  have  been  known  and 
worked  before  copper  or  bronze,  which  archaeologists  say  were 
the  first  metals  to  be  used.  The  metallurgists  say  that  the 
absence  of  iron  implements  as  old  as,  or  older  than,  existing 
copper  and  bronze  ones  is  due  mainly  to  the  rapidity  with  which 
iron  is  destroyed  by  corrosion,  and  the  freedom  from  corrosion 
of  bronze.  Another  reason,  they  say,  is  that  some  people  con- 
sidered iron  an  impure  metal,  so  that  it  could  not  be  used  in  the 
burial  rites,  while  the  copper  and  bronze  vessels  thus  used  con- 
stitute some  of  our  earliest  relics.  These  metallurgists  also 
say  that  the  use  of  iron  must  at  least  equal,  if  not  antedate,  the 
use  of  copper  and  bronze,  because  of  the  greater  metallurgical 
skill  necessary  to  work  the  latter  successfully,  and  also  because 
few  places  contain  both  copper  and  tin  ores;  but  the  probability 
is  that  both  copper  and  iron  were  used  in  different  places  at  the 
same  time,  and  that  the  use  of  bronze  was  developed  later. 

Analyses  of  the  iron  of  prehistoric  weapons  show  that  many 
of  the  earliest  specimens  of  iron  manufacture  contain  consid- 
erable nickel.  This  particular  combination  does  not  occur  in 
any  known  ores,  but  is  invariably  found  in  meteoric  iron.  It  is 
thought  by  some  that  these  weapons  may  have  been  manu- 
factured from  meteorites  that  had  fallen  to  the  earth  long  be- 


MANUFACTURING  PROCESSES  II 

fore  prehistoric  man  had  learned  how  to  dig  for  and  smelt  iron 
in  any  of  the  forms  of  ore  found  on  this  planet. 

Early  Furnaces.  —  The  first  iron  furnaces  were  little  more 
than  holes  in  the  ground,  about  two  feet  square  and  two  feet 
deep,  in  which  the  ore  and  fuel  were  placed.  The  resulting 
product  was  a  lump  of  pasty  iron  that  was  pulled  out  of  the  hole 
and  worked  into  the  desired  shape  under  the  hammer.  The 
smith  made  his  own  charcoal  from  the  surrounding  woods. 
The  method,  however,  was  wasteful  of  iron,  fuel,  and  labor,  and 
the  cast  iron  and  " natural"  steel  produced  by  the  carburizing 
action  of  the  fuel  were,  for  a  long  time,  looked  upon  as  unde- 
sirable products.  Later,  the  smith  learned  how  to  convert  these 
into  wrought  iron,  by  remelting  them  in  the  fire,  and,  at  the 
same  time,  exposing  them  to  the  blast  in  such  a  way  that  most 
of  the  carbon  was  burned.  Wood  and  charcoal  were  the  only 
fuels  available,  so  that  the  size  of  the  plant  was  limited.  As 
soon  as  the  trees  in  the  immediate  vicinity  were  burned,  it  was 
necessary  to  haul  the  fuel  a  long  distance. 

The  draft  required  to  furnish  the  heat  necessary  to  melt  the 
metal  was  obtained  by  placing  the  hearth  or  furnace  upon  the 
top  of  a  hill  or  in  a  valley,  through  which  strong  air-currents 
frequently  passed.  Later,  the  hearths  were  placed  at  the  small 
end  of  wide-mouthed,  tapering,  covered  channels  built  on  the 
windward  side  of  hills.  The  blast  produced  by  these  natural 
currents  of  air,  however,  was  most  uncertain,  so  that  artificial 
means  of  producing  the  blast  were  devised.  The  first  bellows 
were  probably  made  from  the  skins  of  goats.  Valves  for  the 
bellows  were  devised  about  the  fourth  century. 

About  the  fourteenth  century,  German  metallurgists,  seeking 
to  reduce  the  fuel  consumption  and  the  labor  cost,  increased  the 
size  of  the  forge,  especially  the  height,  until  it  was  necessary  to 
drive  the  blast  by  water  power.  The  use  of  this  power,  in  turn, 
made  it  possible  to  increase  still  farther  the  size  of  the  furnace. 
Because  of  this  improvement  in  iron-making,  the  iron  industry 
developed  so  rapidly  that,  in  1558,  an  act  was  passed,  in  England, 
forbidding  the  cutting  of  wood  for  iron-making  in  certain  parts 
of  the  country.  This  was  done  in  order  that  the  navy  would 


12  IRON  AND   STEEL 

not  be  destroyed  by  the  scarcity  of  wood  for  shipbuilding.  In 
1584,  the  building  of  additional  iron  works  in  Surrey,  Kent, 
and  Sussex  was  forbidden.  By  1756,  the  scarcity  of  wood  in 
England  became  so  great  that  iron  was  sought  in  North  America; 
while,  in  1750,  Parliament  prohibited  the  making  of  any  steel  or 
bar  iron  in  England  on  the  grounds  that  these  works  were  a 
common  nuisance. 

Meanwhile,  efforts  were  made  to  use  coal  as  a  fuel,  but  the 
high  sulphur  content  and  the  opposition  of  the  charcoal  makers 
prevented  the  adoption  of  this  fuel  until  1735.  Dud  Dudley 
made  both  wrought  iron  and  cast  iron  with  coal  in  1619,  but  his 
methods  were  never  adopted  by  others.  In  1735,  Abraham 
Darby  began  to  use  coke  as  a  fuel.  Failing  in  his  attempt  to 
use  the  raw  coal,  he  burnt  the  coal  in  heaps  on  the  ground  just 
as  wood  was  burned  to  make  charcoal.  The  iron  made  in  the 
charcoal  blast  furnace  was  low  in  silicon  and  sulphur.  As  the 
iron  made  with  the  coke  blast  furnace  was  higher  in  sulphur, 
the  temperature  of  the  blast  was  increased,  with  the  result  that 
the  sulphur  was  eliminated,  but  a  higher  silicon  content  was 
obtained.  At  first,  it  was  attempted  to  reduce  the  silicon  in  one 
operation,  and  then  burn  the  cinder  and  complete  the  refining  on 
the  same  hearth.  This  method  later  developed  into  the  South 
Wales  process,  in  which  the  two  operations  were  effected  on 
different  parts  of  the  hearth. 

In  an  effort  to  use  coal  or  coke  for  the  conversion  of  cast  iron 
into  wrought  iron,  Henry  Cort  patented  the  reverberatory  fur- 
nace, in  1784.  In  this  furnace,  the  iron  lies  in  a  chamber  apart 
from  the  burning  fuel,  and  is  thus  protected  from  the  carbur- 
izing  action  of  the  fuel  heated  by  the  flame  that  the  fuel  gives 
out.  The  first  bottoms  were  made  of  sand,  with  the  result  that 
the  furnace  was  slow-working,  and  it  was  necessary  to  use  an 
iron  low  in  silicon.  Later,  air-cooled,  cast-iron  bottoms  were 
placed  beneath  the  sand-working  bottoms.  With  these  furnaces, 
the  iron  loss  was  very  great,  but  it  was  largely  offset  by  the 
cheap  fuel  the  furnace  made  available.  Since  1830,  however, 
the  pig-boiling  process,  invented  by  Joseph  Hall,  has  been  the 
principal  method  used  for  producing  wrought  iron,  and  is,  today. 


MANUFACTURING  PROCESSES  13 

known  by  the  term  "puddling."  The  reverberatory  furnace 
for  puddling  has  remained  unchanged,  except  for  an  increase  in 
size  and  the  arrangement  of  a  double  furnace  which  may  be 
worked  from  each  side. 

A  century  ago,  when  charcoal  was  used,  about  five  tons  were 
required  to  produce  a  ton  of  pig  iron;  today,  furnaces  in  Sweden 
consume  considerably  less  than  one  ton.  With  coal  it  took  from 
eight  to  ten  tons  to  smelt  the  ore  for  one  ton  of  pig  iron;  today, 
the  coke  needed  to  do  the  same  work  can  be  made  from  one  and 
one-half  ton  of  coal. 

Development  of  Steel-making.  —  Prior  to  the  development  of 
the  blast  furnace,  steel  was  generally  produced  by  heating,  in 
a  bed  of  charcoal,  iron  bars  made  directly  from  the  ore,  and 
converting  them  into  steel  by  deep  casehardening.  Later,  the 
cementation  process  was  used.  This  steel,  however,  was  not 
always  uniform  in  structure  and  contained  a  considerable  amount 
of  cinder  and  slag.  Benjamin  Huntsman,  therefore,  about  1740, 
devised  the  method  of  melting  steel  in  small  covered  pots, 
or  crucibles,  in  which  wood  or  charcoal  was  placed.  By  this 
method,  the  iron  absorbs  no  impurities  from  the  fire,  but  absorbs 
the  necessary  carbon  from  the  wood  or  charcoal.  The  method, 
however,  is  too  costly,  except  for  steel  that  must  be  of  the  best 
quality.  Most  steel  is  now  made  by  either  the  Bessemer  or  the 
open-hearth  processes,  and  the  use  of  the  electric  furnace  is 
rapidly  growing,  especially  when  a  high  grade  of  steel  is  desired. 
Since  the  development  of  these  processes,  special  attention  has 
been  given  to  the  development  of  steel  for  special  purposes, 
with  the  result  that  steel  may  now  be  had  that  is  suitable  for 
nearly  any  service  desired. 

Strength  of  Iron  and  Steel.  —  The  strength  of  iron  and  steel 
varies  considerably  according  to  the  quality  of  the  material 
and  the  treatment  to  which  it  has  been  subjected.  Generally 
speaking,  cast  iron  may  be  assumed  to  have  a  tensile  strength 
of  15,000  pounds  per  square  inch,  a  compressive  strength  of  80,000 
pounds,  and  a  modulus  of  elasticity  of  12,000,000.  Wrought 
iron  may  have  a  tensile  strength  of  from  40,000  to  5o;ooo  pounds 
per  square  inch,  a  compressive  strength  of  from  40,000  to  45 ,000 


14  IRON  AND  STEEL 

pounds  per  square  inch,  and  a  modulus  of  elasticity  of  27,000,000. 
Bessemer  and  open-hearth  mild  steels  have  a  tensile  strength 
of  about  60,000  pounds  per  square  inch,  and  a  compressive 
strength  of  practically  the  same  value,  with  a  modulus  of  elas- 
ticity of  29,000,000.  This  class  of  steel  is  that  used  as  struc- 
tural steel  for  beams,  etc.,  or  as  boiler  steel  for  plates.  Struc- 
tural steel  for  rivets  is  assumed  to  have  a  tensile  and  compres- 
sive strength  of  about  55,000  pounds  per  square  inch,  and 
boiler  steel  for  rivets,  a  tensile  and  compressive  strength  of 
about  50,000  pounds  per  square  inch.  Spring  steel  of  the  best 
quality  may  have  a  .tensile  and  compressive  strength  of  up  to 
125,000  pounds  per  square  inch.  Alloy  steels  are  still  stronger, 
according  to  their  composition  and  heat- treatment.  Steel  wire 
varies  in  strength  according  to  its  condition  and  quality.  An- 
nealed steel  wire  has  a  tensile  strength  of  80,000  pounds  per 
square  inch;  unannealed  steel  wire,  120,000  pounds  per  square 
inch;  crucible  wire,  180,000  pounds  per  square  inch;  suspension- 
bridge  wire,  200,000  pounds  per  square  inch;  plow-steel  wire, 
270,000  pounds  per  square  inch;  and  piano  wire,  300,000  pounds 
per  square  inch.  High-class  wire  is  made  in  fine  sizes  only,  so 
that  these  high  values  for  strength  per  square  inch  would  not 
apply  to  a  bar  actually  one  inch  square,  but  only  when  fine 
wire  is  drawn  from  the  metal.  Annealed  iron  wire  has  a  ten- 
sile strength  of  about  60,000  pounds  per  square  inch,  and  unan- 
nealed iron  wire,  80,000  pounds  per  square  inch.  Steel  castings 
are  produced  in  different  grades,  but  may  be  assumed  to  have  a 
strength  of  about  70,000  pounds  per  square  inch,  both  in  ten- 
sion and  compression.  These  values,  of  course,  are  all  ultimate 
strengths,  and  a  reasonable  factor  of  safety  must  always  be 
adopted,  as  outlined  in  text-books  on  the  strength  of  materials 
or  in  handbooks  covering  this  subject. 

Varying  temperatures  have  a  decided  effect  upon  the  strength 
of  iron  and  steel.  Intense  cold  raises  the  limit  of  elasticity  of 
both  iron  and  steel,  but  does  not  affect  their  tensile  strength. 
It  reduces  their  resistance  to  impact,  however.  With  a  rising 
temperature  from  that  of  the  normal  temperature  of  70  degrees 
F.,  there  is  first  an  increase  in  strength  and  then  a  rapid  drop. 


MANUFACTURING  PROCESSES  15 

If  wrought  iron  is  assumed  to  have  a  strength  of  100  per  cent 
at  70  degrees  F.,  its  strength  at  400  degrees  F.  is  about  112 
per  cent  and  at  570  degrees  F.,  116  per  cent,  after  which  there  is 
a  falling  off,  so  that  the  strength  at  750  degrees  F.  is  96  per 
cent,  and  at  noo  degrees  F.,  42  per  cent.  Cast  iron  retains  its 
strength  of  100  per  cent  up  to  400  degrees  F.,  but  falls  from  this 
point  to  92  per  cent  at  750  degrees  F.  and  42  per  cent  at  noo 
degrees  F.  Structural  steel  has  a  strength  of  132  per  cent  at 
400  degrees  F.,  122  per  cent  at  570  degrees  F.,  86  per  cent  at 
750  degrees  F.,  and  28  per  cent  at  noo  degrees  F.  Cast  steel 
has  its  highest  value  of  strength  of  125  per  cent  at  400  degrees  F., 
which  is  reduced  to  121  per  cent  at  570  degrees  F.,  to  97  per  cent 
at  750  degrees  F.,  and  to  57  per  cent  at  930  degrees  F.  These 
figures  are,  of  course,  subject  to  variation,  but  are  given  in  order 
to  indicate  the  probable  weakening  of  various  irons  and  steels 
with  increasing  temperatures. 


CHAPTER  II 
IRON   ORE  AND   ITS  PREPARATION  FOR  SMELTING 

AN  ore  is  a  material  that  contains  a  metal  in  such  quantities 
that  it  may  be  mined  and  worked  commercially  for  that  metal. 
In  an  ore,  the  metal  usually  is  contained  in  chemical  combina- 
tion with  some  other  element,  and,  in  addition,  there  are  gener- 
ally various  impurities;  hence,  the  condition  in  which  the  metal 
exists  in  the  ore  differs  greatly.  In  all  commercial  iron  ores,  the 
metal  occurs  as  an  oxide,  a  carbonate,  or  a  sulphide.  The  ore 
may  be  deposited  in  beds,  lenses,  or  veins.  Beds  are  masses  of 
minerals  found  in  solid  stratas;  lenses  or  pods  are  irregular 
masses  of  ore  imbedded  in,  and  separated  by,  earth  or  rock; 
veins  fill  crevices  or  seams  and  generally  have  quite  well-defined 
walls.  Ores  having  a  high  metal  content  are  termed  "rich"; 
those  having  a  low  metal  content  are  termed  "lean." 

Commercial  iron  ore  —  oxide,  carbonate,  or  sulphide  of  iron 
—  contains  from  about  35  to  70  per  cent  of  iron,  together  with 
impurities  of  phosphorus,  silica  (sand),  etc.  The  highest  class 
of  iron  ore,  when  pure,  contains  72.4  per  cent  of  iron.  When  it 
contains  less  than  40  per  cent  of  iron,  it  must  first  be  concen- 
trated, and  when  it  contains  less  than  25  per  cent  of  iron,  it  is 
not  considered  of  any  commercial  value,  because  the  cost  of 
extracting  the  iron  from  the  ore  is  too  high  to  make  it  possible 
to  sell  the  product  in  competition  with  that  extracted  from 
richer  ores.  The  iron  ores  mined  in  the  United  States  at  the 
present  time  contain  on  an  average  slightly  more  than  50  per 
cent  of  iron.  Those  mined  in  the  Lake  Superior  district,  how- 
ever, sometimes  contain  over  60  per  cent  of  iron.  The  best 
iron  ores  are  those  in  which  the  iron  is  combined  with  oxygen, 
forming  an  oxide  ore.  Ores  which  consist  of  carbonates,  that 
is,  minerals  in  which  the  iron  is  present  in  combination  with 
carbon  and  oxygen,  are  also  mined,  and  are  of  considerable  im- 

16 


IRON  ORE  17 

portance,  although  they  must  be  roasted  to  drive  off  the  car- 
bonic acid.  The  sulphide  ores,  that  is,  minerals  in  which  the 
iron  is  present  in  combination  with  sulphur,  are  also  used,  but 
are  of  minor  importance.  These  ores  must  be  desulphurized  in 
order  to  eliminate  the  sulphur.  In  fact,  all  iron  ores,  whether 
sulphides  or  otherwise,  which  contain  sulphur  to  an  amount 
exceeding  one  per  cent,  must  be  subjected  to  a  special  treatment 
before  smelting.  The  three  most  important  iron  ores  consist- 
ing of  iron  oxides  are  magnetite,  hematite,  and  limonite.  The 
carbonate  iron  ore  is  known  as  siderite  and  the  sulphide  iron  ore 
as  pyrite. 

Magnetite  Ore.  —  Magnetite,  the  chemical  symbol  of  which 
is  Fe304,  contains,  when  pure,  72.4  per  cent  of  iron.  In  this  ore, 
the  iron  is  present  as  a  magnetic  oxide,  and  it  owes  its  name  to 
the  fact  that  it  is  attracted  by  the  magnet.  Magnetite  ore 
deposits  are  often  located  by  the  attraction  they  assert  upon 
the  magnetic  needle.  In  large  deposits,  magnetite  generally 
occurs  in  massive  crystalline  form.  It  is  also  found  as  sand,  but 
metallurgists  prefer  not  to  use  these  sands  when  it  can  be  avoided. 
Magnetite  is  the  purest  form  of  iron  ore  found  in  nature  and 
contains  the  largest  percentage  of  iron  obtainable  in  any  ore. 
It  has  practically  the  same  composition  as  the  black  scale  formed 
on  iron  heated  above  a  red  heat,  and  when  pure  is  almost  black. 
Commercial  magnetite  ores,  however,  generally  contain  some 
impurities  such  as  sulphur,  phosphorus,  and  titanium,  and  these 
ores  vary  in  color  through  a  range  of  shades  from  black  to  blue- 
black,  steel  gray,  or  slightly  green.  Sometimes  the  ore  is  mixed 
with  such  a  large  proportion  of  rock  that  the  actual  percentage 
of  iron  for  a  given  weight  is  comparatively  small,  and  such  ore 
may  prove  too  lean  for  economical  smelting.  As  a  rule,  magne- 
tite ore  containing  titanium  has  not  been  used  for  iron  smelting, 
but  of  recent  years  experiments  have  been  made  which  indicate 
that  magnetite  carrying  titanium  is  not  necessarily  objection- 
able. As  there  are  very  large  deposits  of  these  ores  in  many 
parts  of  the  world,  it  is  possible  that  the  world's  commercial 
ore  supply  will,  in  the  future,  be  increased  by  these  deposits  of 
titanium  carrying  magnetite  ores. 


1 8  IRON  AND  STEEL 

Magnetite  has  a  hardness  of  from  5  to  6.5  on  the  Mohs'  hard- 
ness scale.  It  produces  a  black  streak  on  an  unglazed  porcelain 
plate.  The  specific  gravity  varies  from  4.9  to  5.2.  As  a  rule, 
magnetite  ores  do  not  contain  any  water  in  combination  —  that 
is,  they  are  practically  anhydrous,  and  whatever  moisture  they 
contain  is  driven  off  by  heating  them  to  a  temperature  of  212 
degrees  F. 

Magnetite  ore  is  found  in  many  parts  of  the  world.  There 
are  rich  magnetite  deposits  in  the  United  States  in  Pennsyl- 
vania, New  York,  and  New  Jersey,  and  these  supplied  the  most 
of  the  American  iron  before  the  discovery  of  the  hematite  ore 
deposits  in  the  Lake  Superior  region.  The  ores  in  the  Cornwall 
ore  hills  of  Pennsylvania  also  contain  copper,  which  is  recovered 
and  through  which  the  cost  of  the  iron  obtained  from  that  bed 
is  greatly  reduced.  Large  deposits  of  magnetite  ore  are  also 
found  in  several  of  the  other  states.  The  extensive  iron  ore 
deposits  in  Sweden  are  largely  magnetite,  and  the  well-known 
Dannemora  iron  is  made  from  magnetite  smelted  with  charcoal. 

Red  Hematite  Ore.  —  There  are  several  varieties  of  hematite 
ore,  but  the  one  generally  known  by  this  name  is  red  hematite, 
which  is  an  iron  oxide  containing,  when  pure,  70  per  cent  of 
iron,  and  having  the  chemical  symbol  Fe203.  The  commercial 
hematites  are  not  pure,  however,  the  richest  obtained  in  the 
regular  mining  being  those  of  the  Lake  Superior  district,  which 
contain  a  maximum  of  64  per  cent  of  pure  iron  and  average 
about  60  per  cent.  In  addition  to  the  hematite  ore  obtained 
in  the  Lake  Superior  district,  this  ore  is  mined  in  many  parts  of 
the  United  States  and  in  Cuba,  Canada,  Newfoundland,  Spain, 
Germany,  and  England.  Approximately  93  per  cent  of  the 
iron  ore  mined  in  the  United  States  is  hematite  ore.  The  ore 
is  hard  or  soft,  depending  upon  whether  it  is  found  in  massive 
compact  rock-like  formation  or  in  loose  and  earthy  substances. 
The  color  varies  from  a  bluish-gray  to  a  deep  red,  but  the  name 
"red  hematite"  is  due  to  the  fact  that  the  ore  always  gives  a  red 
streak  on  an  unglazed  porcelain  plate.  The  hardness  on  the 
Mohs'  scale  varies  from  5.5  to  6.5,  and  the  specific  gravity, 
from  4.2  to  5.3.  Hematite  ore  is  anhydrous  —  that  is,  it  con- 


IRON  ORE  19 

tains  no  water  in  combination,  any  moisture  contained  being 
driven  off  by  exposing  the  ore  to  a  temperature  of  212  de- 
grees F. 

Brown  Hematite.  —  Brown  hematite  is  an  iron  oxide  con- 
taining water  in  combination,  and  may  be  converted  into  red 
hematite  by  roasting.  When  pure,  it  contains  from  60  to  65 
per  cent  of  iron,  but  the  commercial  hematite  ores  contain  only 
from  35  to  55  per  cent  of  iron.  As  a  rule,  ores  of  this  kind  carry 
a  larger  percentage  of  gangue  (rocky  or  sandy  non-metallic  sub- 
stances) than  red  hematite.  The  brown  hematite  often  con- 
tains manganese  and  usually  so  much  phosphorus  that  it  cannot 
be  used  for  the  Bessemer  process,  but  it  seldom  contains  enough 
sulphur  to  cause  any  trouble  on  that  account.  Brown  hema- 
tite ore  is  found  in  beds  and  veins  and  often  forms  the  cover  of 
copper  ores.  It  is  generally  porous  and  easy  to  reduce  and 
smelt  in  a  blast  furnace.  It  is  often  found  in  clay  deposits,  and 
the  material  mined  must  then  be  washed  in  order  to  remove  the 
clay  and  gravel. 

Limonite.  —  Of  the  brown  hematite  ores,  limonite,  the  chemi- 
cal formula  of  which  is  2  Fe2O3  +  3  H20,  is  one  of  the  most  im- 
portant. The  color  of  this  ore  varies  from  light  brown  to  black. 
It  gives  a  yellowish-black  streak  on  an  unglazed  porcelain  plate. 
The  hardness  on  the  Moris'  hardness  scale  varies  from  5  to  5.5, 
and  the  specific  gravity,  from  3.6  to  4.  Limonite  may  be  found 
as  "  compact,"  which  occurs  in  various  massive  forms;  "ocher- 
ous"  or  "  ear  thy,"  which  varies  from  brown  to  ocher  yellow  in 
color  and  is  frequently  mixed  with  clay;  ''bog  iron  ore,"  which 
is  formed  in  marshy  places  and  is  loose  and  porous  in  texture; 
and  " brown  clay"  or  " iron-stone,"  which  occurs  in  compact 
masses. 

Turgite.  —  Turgite  is  another  ore  generally  classed  as  a  brown 
hematite.  Its  chemical  composition  is  2  Fe203  +  H2O.  When 
pure,  it  contains  66  per  cent  of  iron.  Its  color  is  brown  or  yel- 
low, with  a  brown  or  brownish-yellow  streak  on  an  unglazed 
porcelain  plate.  The  hardness  on  the  Mohs'  hardness  scale 
varies  from  2.5  to  5.5,  and  the  specific  gravity  varies  from 
3  to  4-7- 


20  IRON  AND   STEEL 

Goethite.  —  Goethite  is  another  ore  generally  grouped  as  a 
brown  hematite.  Its  chemical  composition  is  Fe2O3  +  H20. 
When  pure,  it  contains  63  per  cent  of  iron.  It  has  the  same 
appearance,  color,  and  streak  as  turgite,  and  has  practically  the 
same  hardness  and  specific  gravity. 

Oolitic  Ore.  —  Oolitic  ore  is  another  variety  of  brown  hema- 
tite. It  occurs  in  small  granules  somewhat  like  fish  eggs 
cemented  together  with  clay,  or  in  siliceous  materials,  or  the 
grains  are  foreign  matter  cemented  together  by  the  iron  ore. 
When  the  gangue  is  siliceous,  this  ore  is  usually  of  little  value; 
but  when  the  gangue  is  basic,  the  ore  may  be  quite  valuable, 
even  when  low  in  iron. 

Brown  hematite  ores  are  found  in  several  parts  of  the  United 
States,  and  in  Cuba,  Spain,  Germany,  England,  and  France. 
Most  of  the  Spanish  and  Cuban  ores  are  of  the  brown  hematite 
kind. 

Carbonate  Iron  Ore.  —  The  carbonate  iron  ore,  the  chemical 
symbol  of  which  is  FeC03,  is  the  least  desirable  of  the  generally 
used  iron  ores.  When  pure,  it  contains  48.3  per  cent  of  iron, 
but  the  deposits  usually  include  so  much  barren  material  that 
the  ore  must  be  washed.  This  ore  is  frequently  known  as 
"siderite"  or  "  spathic  ore."  British  ores  of  this  kind  are  fre- 
quently also  known  as  " black  band,"  when  containing  bitu- 
minous matter,  as  in  coal  seams,  and  "clay  band"  or  '  clay 
iron-stone,"  when  found  in  clay  deposits  or  occurring  in  shales 
in  conjunction  with  much  clay.  This  ore  must  often  be  roasted 
before  it  is  charged  into  the  blast  furnace,  in  order  to  expel  the 
carbon  dioxide.  The  color  of  the  carbonate  iron  ore  varies 
from  a  brown  or  yellow-brown  to  a  gray.  Its  hardness  on  the 
Mohs'  hardness  scale  varies  from  3.4  to  4.5,  and  the  specific 
gravity  varies  from  3.7  to  3.9.  Carbonate  iron  ores  are  found, 
to  some  extent,  in  the  United  States,  but  are  more  commonly 
mined  in  Great  Britain,  Germany,  Hungary,  and  Russia.  They 
are  of  especial  importance  in  England  and  Scotland,  where  they 
form  an  important  factor  in  the  pig-iron  industry.  Black- 
band  ore  produces  strong  iron  and,  when  mixed  with  hematite 
ore,  produces  a  soft,  good  grade  of  Scotch  iron. 


IRON  ORE  21 

Iron  Ores  of  Minor  Importance.  —  Among  the  iron  ores  of 
minor  importance  may  be  mentioned  pyrite,  ilmenite,  and  frank- 
linite.  Pyrite,  the  chemical  symbol  of  which  is  FeS2,  is  a  sul- 
phide of  iron,  the  pure  ore  containing  46.7  per  cent  of  the  metal. 
Because  of  its  great  sulphur  content,  this  ore  cannot  be  smelted 
directly,  but  is  first  desulphurized,  sulphuric  acid  being  extracted 
from  the  ore  and  forming  an  important  part  of  the  product. 
The  residue  from  the  manufacture  of  the  sulphuric  acid,  known 
as  "blue  billy"  or  "purple  ore,"  is  used  in  the  manufacture  of 
low-phosphorus  iron.  This  ore  often  also  contains  copper,  and 
after  the  sulphuric  acid  has  been  extracted,  this  metal  is  then 
first  obtained  by  means  of  the  so-called  "wet"  process,  after 
which  the  ore  finally  is  used  as  an  iron  ore.  Pyrite  has  a  yellow 
color  and  produces  a  green  or  brownish-black  streak  on  an  un- 
glazed  porcelain  plate.  The  hardness  on  the  Mohs'  hardness 
scale  varies  from  6  to  6.5,  and  the  specific  gravity,  from  4.8  to 
5.2.  While,  at  the  present  time,  this  ore  is  of  minor  importance, 
it  is  likely  that,  when  the  deposits  of  the  rich  oxide  ores  have 
been  exhausted,  it  will  become  of  great  importance  in  the  iron 
industry,  because  there  are  very  large  deposits  available  of  sul- 
phide ores. 

Ilmenite,  or  titanic  iron  ore,  is  an  iron  oxide  ore  containing 
titanium.  Deposits  of  this  ore  are  found  in  the  United  States, 
in  the  Adirondack  Mountains,  and  in  Canada,  New  Zealand, 
Sweden,  and  Norway.  Until  recently,  these  ores  have  not  been 
considered  to  be  of  any  commercial  importance  on  account  of 
the  furnace  troubles  usually  met  with  when  smelting.  Re- 
cently, however,  ores  of  this  kind  have  been  successfully  used. 

Franklinite  is  a  magnetite  ore  containing  zinc  and  manganese. 
After  the  zinc  has  been  extracted  from  the  ore,  the  residue  is 
used  for  making  spiegeleisen,  a  pig  iron  containing  about  20 
per  cent  of  manganese.  Only  one  large  deposit  of  this  ore  is 
known;  this  is  located  in  New  Jersey. 

Factors  Determining  the  Value  of  an  Iron  Ore.  —  The  value 
of  an  iron  ore  depends  not  only  upon  the  iron  content,  but  upon 
the  impurities  and  the  cost  of  mining  and  smelting.  Because  of 
the  cost  of  transporting  it  to  the  nearest  market,  lean  ore  has 


22  IRON  AND   STEEL 

been  used  in  the  Lake  Superior  region  as  ballast  for  railroads; 
this  same  ore  would  have  been  considered  valuable  in  other 
states,  where  the  fuel  supply  and  market  are  close  at  hand. 
In  Alabama,  ores  containing  about  38  per  cent  of  iron  are  used, 
because  the  gangue  contains  so  much  lime  that  less  flux  is 
required  in  the  furnace;  besides,  it  is  mined  close  to  centers  of 
pig  iron  production  and  extensive  coal  fields.  An  ore  may 
even  be  too  rich  to  work  satisfactorily  by  itself,  as  it  may  not 
have  enough  gangue  to  furnish  a  sufficient  volume  of  slag; 
although  the.  usual  trouble  is  to  obtain  a  mixture  that  is  rich 
enough  in  iron. 

The  value  of  an  ore  also  depends  upon  the  product  .desired,  as 
an  ore  that  is  not  at  all  suitable  for  one  purpose  may  be  entirely 
satisfactory  for  another;  also,  an  ore  that  is  not  suitable,  when 
used  alone,  may  be  very  desirable  for  mixing  with  another. 
The  value  of  an  ore  is  also  effected  by  the  physical  character- 
istics. The  red  hematites  are  most  desirable,  because  they  are 
open  and  porous,  and,  therefore,  are  more  easily  reduced  than 
the  magnetite  ores,  which,  while  richer,  are  denser.  The  hema- 
tites are  also  less  likely  to  carry  objectionable  elements,  such  as 
sulphur  or  titanium.  Fine  ores  are  undesirable,  because  they 
are  more  difficult  to  handle  and  transport,  and  because  they  are 
very  likely  to  cause  irregular  working  in  the  blast  furnace  as 
well  as  considerable  loss  from  the  formation  of  flue-dust.  The 
amount  of  moisture  in  the  ore  is  also  an  important  factor  in  the 
determination  of  the  value  of  the  ore,  for  besides  increasing  the 
cost  of  transportation  this  water  must  be  driven  off  in  the  blast 
furnace  operation,  which  necessitates  greater  fuel  consumption. 
The  present  practice  is  to  market  all  ores  according  to  their 
composition,  when  dried  at  a  temperature  of  212  degrees  F. 

If  the  chemical  composition  of  an  iron  ore  is  known,  the 
approximate  proportion  of  iron  that  it  contains  may  be  deter- 
mined by  multiplying  the  percentage  of  the  oxide  Fe2O3  by  0.7; 
or  the  percentage  of  the  oxide  Fe3O4  by  0.72;  or  the  percentage 
of  the  carbonate  FeCO3  by  0.48.  The  product  thus  obtained 
gives  the  percentage  of  metallic  iron  actually  contained  in  the 
ore. 


IRON  ORE  23 

Influence  of  Various  Elements  on  Iron  Ore.  —  The  various 
iron  ores  when  mined  are  seldom  pure  oxides,  carbonates,  or 
sulphides,  but  are,  on  the  other  hand,  generally  mixed  with 
mineral  matter  such  as  quartz,  limestone,  and  clay  containing 
no  iron  or  other  metallic  components.  These  impurities  are 
generally  known  by  the  inclusive  name  "gangue."  In  addition, 
a  great  number  of  other  elements  are  found  in  combination 
with  the  ore,  such  as  sulphur,  phosphorus,  manganese,  titanium, 
copper,  and  nickel,  as  well  as  alumina,  magnesia,  silica,  and 
lime.  Of  the  impurities,  sulphur  and  phosphorus  are  the  most 
common  and,  on  account  of  their  influence,  the  most  important. 

Influence  of  Sulphur  on  Iron  Ore.  —  Sulphur  is  objectionable 
in  an  iron  ore  because  it  must  be  removed  in  the  blast  furnace 
by  the  use  of  additional  flux,  provided  it  occurs  in  excessive 
amounts.  The  use  of  an  additional  flux  requires  an  increased 
fuel  consumption  and  results  in  a  decreased  output;  hence,  it 
is  generally  considered  advantageous  to  reduce  the  amount  of 
sulphur  in  the  ore  by  roasting  it  before  the  ore  is  fed  to  the  blast 
furnace.  If  the  sulphur  in  the  ore  cannot  be  readily  oxidized, 
the  ore  cannot  be  used  for  the  making  of  iron  or  steel,  no  matter 
how  desirable  it  otherwise  might  seem.  Sulphur  is  generally 
considered  objectionable  in  all  classes  of  iron  and  steel,  if  present 
beyond  certain  small  percentages,  and  steel  specifications  usu- 
ally require  a  low  sulphur  content. 

Influence  of  Phosphorus  on  Iron  Ore.  —  The  percentage  of 
phosphorus  allowable  in  an  ore  before  it  passes  to  the  blast 
furnace  depends  upon  the  purpose  for  which  the  pig  iron  made 
from  the  ore  is  to  be  used.  For  basic  steel-making  or  for  foundry 
purposes,  the  ore  may  contain  0.5  per  cent  of  phosphorus  to 
each  100  per  cent  of  iron  and  still  be  satisfactory.  Phosphorus 
in  moderate  amounts  is  desirable  in  pig  iron  intended  for  cast- 
iron  foundries.  Ore  of  this  kind,  however,  cannot  be  used  if 
the  metal  is  intended  for  the  making  of  Bessemer  steel.  On 
account  of  the  impossibility  of  using  high-phosphorus  ores  for 
the  Bessemer  process,  therefore,  iron  ores  have  been  divided 
into  two  classes,  Bessemer  and  non-Bessemer  ores.  As  Bessemer 
pig  iron  must  not  contain  over  one  part  of  phosphorus  to 


24  IRON  AND   STEEL 

1000  parts  of  iron  (o.i  per  cent),  and  as  the  phosphorus  in  the 
fuel  and  limestone  used  in  the  blast  furnace  also  enters  the  pig 
iron,  the  practical  limit  for  the  presence  of  phosphorus  in  an 
iron  ore  that  is  to  be  used  for  making  Bessemer  steel  is  limited 
to  0.07  per  cent  of  phosphorus,  or  one  part  of  phosphorus  to 
1400  parts  of  iron.  Non-Bessemer  ores  do  not,  as  a  rule,  com- 
mand as  high  a  price  as  Bessemer  ores,  even  when  they  contain 
the  same  percentage  of  iron.  Sometimes  high-grade  Bessemer 
ores  are  mixed  with  non-Bessemer  ores  in  order  to  produce  a 
mixture  which  will  contain  so  small  a  percentage  of  phosphorus 
that  the  mixture  may  be  classed  as  a  Bessemer  ore.  In  ores 
intended  for  making  open-hearth  steel,  a  higher  percentage  of 
phosphorus  may  be  present  than  in  the  ores  intended  for  Bes- 
semer steel,  but  as  low  a  percentage  of  phosphorus  as  possible  is 
preferable  in  either  case.  Some  special  low-phosphorus  pig  iron 
used  in  steel-making  is  made  from  selected  ores  and  generally 
commands  a  higher  price. 

Richness  of  Commercial  Iron  Ore.  —  The  present  tendency 
in  the  manufacture  of  iron  is  to  use  ores  that  are  less  rich  than 
those  used  in  the  past,  partly  because  of  the  scarcity  of  the 
richer  ores,  and  also  because  of  the  improved  methods  in  min- 
ing, transportation,  and  smelting,  which  make  the  leaner  ores 
available.  The  richness  of  the  iron  ore  used  in  various  coun- 
tries is  indicated  by  referring  to  the  amount  of  ore  required  to 
produce  one  ton  of  pig  iron.  In  the  United  States,  for  example, 
an  average  of  1.9  ton  of  ore  is  required  to  produce  i  ton  of  pig 
iron;  in  Sweden  and  Russia,  2  tons  of  ore  to  i  ton  of  pig  iron; 
in  Great  Britain  and  Germany,  2.4  tons  of  ore  to  i  ton  of  pig 
iron;  and  in  France  and  Belgium,  2.7  tons  of  ore  to  i  ton  of 
pig  iron.  When  native  British  ores  are  used  alone,  as  much  as 
3  tons  of  ore  are  required  for  each  ton  of  pig  iron. 

Iron  Ore  Deposits.  —  The  early  source  of  iron  ore  appears  to 
have  been  in  India,  although  the  Greeks  obtained  it  from  the 
Chalybes,  who  dwelt  on  the  Southern  coast  of  the  Black  Sea. 
The  Romans  obtained  iron  ore  from  Spain  and  Elba.  At  pres- 
ent, the  United  States  is  the  largest  producer  of  iron  ore  and 
its  ores  are  much  richer  than  those  of  most  European  countries: 


IRON  ORE  25 

however,  the  nearness  of  the  ore  bed  to  the  fuel  supply  and 
the  market  for  the  product  makes  the  working  of  these  leaner 
ores  profitable.  Most  of  the  United  States  ores  are  obtained  in 
the  Lake  Superior  region,  yet  the  yearly  production  of  ore  from 
mines  outside  of  this  region  exceeds  that  of  most  foreign  nations. 
Notwithstanding  the  long  distance  of  the  Lake  Superior  beds 
from  the  fuel  supply,  the  richness  of  the  ores  and  the  efficiency 
of  the  mining  and  ore-handling  methods  have  enabled  this  region 
to  retain  its  supremacy  over  the  Southern  fields,  where  the  iron 
and  fuel  are  close  at  hand.  In  the  later  fields  of  the  Lake 
Superior  region,  the  open-pit  method  of  mining  is  used,  as  the 
ore  lies  in  beds  sometimes  250  feet  thick  that  are  from  a  few  feet 
to  about  100  feet  below  the  surface.  The  ore  is  mined  by  large 
steam  shovels  and  loaded  directly  into  the  cars. 

The  Southern  district,  which  centers  around  Birmingham, 
Alabama,  is  one  of  the  most  advantageous  pig-iron  making  dis- 
tricts in  the  world,  as  it  has  the  ore,  fuel,  and  flux  in  a  closer 
radius  than  any  other;  but  the  ores  and  fuel  are  of  a  compara- 
tively low  quality.  Much  of  the  ore  is  concentrated  by  washing 
and  all  the  ores  carry  a  large  percentage  of  silica. 

Before  the  development  of  the  iron  deposits  of  the  Lake  Supe- 
rior region,  the  principal  American  ores  were  the  rich  magnetites 
of  New  Jersey,  New  York,  and  Pennsylvania.  Magnetic  con- 
centration makes  some  of  this  ore  the  richest  produced.  The 
United  States  also  imports,  in  normal  times,  large  quantities  of 
ore  from  Cuba,  Chile,  Spain,  Sweden,  Canada,  Newfoundland, 
Africa,  and  some  other  countries.  It  exports  a  small  amount 
to  Canada.  The  Cuban  ore  beds  are  stretched  over  large  areas 
and  lie  at  the  surface  so  that  they  require  no  stripping.  Com- 
pared with  the  Lake  Superior  ores,  they  are  of  a  low  grade,  but 
the  cheap  transportation  and  the  mining  methods  available 
make  the  development  of  these  fields  very  desirable.  The  Min- 
ette  region  of  Western  Germany  and  Eastern  France  prior  to  the 
war  supplied  the  ore  for  the  iron  industry  in  those  countries  as 
well  as  for  a  part  of  Belgium.  For  the  most  part,  the  deposit 
is  a  low-grade  oolitic  ore,  having  from  25  to  45  per  cent  of  iron 
rather  high  in  phosphorus.  Norway,  Sweden,  Russia,  and 

2F 


26  IRON  AND  STEEL 

Finland  have  large  deposits  of  magnetite.  The  ore  of  Norway 
and  Sweden  is  of  high  iron  content  and  most  of  it  is  very  desir- 
able for  steel-making.  The  ores  of  Russia  and  Finland  contain 
less  iron.  Great  Britain  has  large  deposits  but,  like  Germany, 
Belgium,  and  France,  imports  large  quantities  of  ore  from  other 
nations.  Spain,  Algeria,  Italy,  and  Greece  produce  more  ore 
than  is  used  within  their  boundaries,  and  China,  Chile,  Brazil, 
Mexico,  and  Venezuela  have  large  undeveloped  deposits. 

Mining  Iron  Ore.  —  The  method  adopted  for  mining  iron  ore 
depends  upon  the  physical  and  geological  conditions  of  the  de- 
posits, their  apparent  extent  and  relation  to  the  surface,  the 
nature  of  the  rocks  or  earthy  materials  with  which  the  ore  occurs, 
and  the  chemical  composition  of  the  mineral  to  be  mined.  It  is 
also  dependent  upon  the  location  of  the  deposit  with  relation  to 
the  market.  Large  continuous  ore  deposits  covered  by  a  com- 
paratively thin  layer  of  unproductive  earth  or  mineral  may  be 
mined  by  either  the  open-cut  or  the  underground  method.  By 
the  open-cut  method,  all  the  ore  is  obtained,  and  expensive  sys- 
tems of  supports  are  unnecessary,  but  the  work  cannot  be  car- 
ried on  in  stormy  weather,  and  large  quantities  of  surface  water 
must  constantly  be  removed.  Besides,  the  mineral  mined  may 
be  saturated  with  water  and  melted  snow,  and  the  material 
removed  from  the  top  of  the  deposit  must  be  disposed  of. 

The  underground  method  has  its  advantages  and  is,  of  course, 
the  only  practicable  way  when  a  deposit  is  covered  to  a  consid- 
erable depth.  By  this  method,  the  ore  is  reached  through  a 
vertical  or  inclined  shaft,  or  through  a  nearly  horizontal  passage 
known  as  an  "adit."  Passages,  termed  " drifts"  or  "levels," 
are  then  driven  through  the  ore  or  the  adjacent  rock  for  the 
transporting  of  the  ore,  which  is  mined  from  rooms  or  "stopes" 
opening  off  from  these.  As  the  openings  are  costly  and  are  to 
be  used  as  long  as  a  deposit  is  being  mined,  they  must  be  care- 
fully located.  While  the  shaft  or  adit  is  frequently  driven  in 
the  ore,  when  possible  it  should  be  driven  in  the  adjacent  rock 
so  as  to  be  free  from  disturbance.  When  driven  in  the  ore, 
sufficient  ore  must  be  left  about  the  opening  to  prevent  its 
destruction. 


IRON  ORE  27 

As  the  ore  is  being  mined,  holes  are  drilled  in  advance  of  the 
underground  workings  to  determine  the  best  way  in  which  to 
work.  These  holes  also  show  how  the  ore  can  be  reached  to  the 
best  advantage  when  lost  through  a  "fault"  or  "slip"  (displace- 
ment or  sliding  of  the  ore  vein)  or  "horse"  (the  infusion  of 
barren  or  lean  metal).  They  also  show  whether  a  vein  that  is 
gradually  growing  thinner  "pinches  out"  (or  ends)  or  at  some 
point  farther  widens  out  again,  so  that  it  may  be  profitably 
worked.  When  the  deposit  dips  considerably,  several  levels  may 
be  worked  at  one  time,  the  upper  level  being  farther  advanced 
than  the  lower.  When  ore  is  mined  above  a  given  level  and 
allowed  to  fall,  by  gravity,  through  chutes  or  otherwise,  the 
method  is  known  as  "over-hand  stoping."  When  the  ore  is 
worked  below  the  given  level  and  is  raised,  the  method  is  termed 
' '  under-hand  stoping ." 

Underground  working  requires  an  expensive  system  of  sup- 
ports, because  the  place  from  which  the  ore  is  mined  must  be 
supported  in  some  manner.  Sometimes  rock  or  waste  is  used 
for  this  purpose,  but  timber  is  most  generally  relied  upon.  This 
material,  however,  is  unsatisfactory,  because  of  its  constantly 
increasing  cost,  the  frequent  renewals  necessary,  owing  to  de- 
cay, and  its  liability  to  catch  fire.  Concrete,  steel,  and  masonry 
have,  therefore,  been  used  in  many  places. 

Iron  Ore  Beneficiation.  —  While  some  ore  may  be  smelted  in 
the  same  condition  as  it  is  mined,  the  ore  in  most  cases  is 
crushed,  so  that  the  lumps  are  fairly  uniform  in  size.  In  addi- 
tion, iron  ore  is  often  treated  in  some  manner  in  order  to  remove 
or  eliminate  valueless  or  objectionable  components.  This  treat- 
ment is  known  by  the  term  "beneficiation,"  which  is  applied 
to  those  processes  used  for  the  improvement  of  iron  ore  which 
result  in  producing  an  ore  containing  a  greater  percentage  of  the 
metal  to  be  extracted  than  the  original  mined  product.  Fre- 
quently the  term  is  also  used  to  designate  those  methods  which 
change  the  physical  and  sometimes  the  chemical  characteristics 
of  the  ore  in  such  a  manner  that  it  will  be  more  suitable  for  the 
production  of  any  one  commercial  iron  or  steel.  Seven  distinct 
methods  for  the  beneficiation  of  iron  ore  are  used,  these  being: 


28  IRON  AND   STEEL 

(i)  hand  picking  or  cobbing;  (2)  washing;'  (3)  jigging;  (4) 
drying;  (5)  roasting;  (6)  magnetic  concentration;  and  (7)  ag- 
glomeration, the  latter  method  being  separated  into  three  other 
distinct  methods:  briquetting,  nodulizing,  and  sintering. 

When  benenciation  produces  a  richer  ore,  it  is  evident  that 
more  than  one  ton  of  raw  material  is  required  to  produce  one 
ton  of  the  beneficiated  ore.  For  example,  an  ore  containing 
40  per  cent  of  iron  may  be  so  concentrated  that  it  leaves  an  ore 
containing  60  per  cent  of  iron,  but  it  is  evident  that  at  least  one 
and  one-half  ton  of  the  4o-per-cent  ore  must  be  used  to  produce 
one  ton  of  the  richer  6o-per-cent  ore.  In  cases  when  only  a 
change  in  the  physical  condition  is  obtained,  the  resulting  prod- 
uct may  be  either  less  or  more  than  the  original  material,  de- 
pending upon  the  process  used.  Except  in  the  case  of  agglomer- 
ation processes,  the  complete  recovery  of  the  iron  content  in 
the  ore  is  seldom  secured  by  benenciation,  because  some  of  the 
metal  is  lost  in  the  waste  or  "  tailings."  In  many  cases,  it  is 
inadvisable  to  continue  the  process  of  benenciation  to  the 
apparently  practical  limit,  because  the  cost  of  the  process  be- 
yond a  certain  point  is  greater  than  the  gain  obtained  through  it. 

The  term  "  benenciation  "  was  formerly  applied  only  to  ores  of 
precious  metals,  such  as  gold,  silver,  and  platinum,  but  at  the 
present  time  it  is  generally  applied  to  the  ores  of  other  metals, 
including  iron  ore. 

Hand  Picking  or  Cobbing.  —  The  first  step  in  the  concentra- 
tion of  an  ore  is  to  roughly  sort  out  the  worthless  material  which 
is  mixed  with  the  ore  as  it  comes  from  the  mines,  and  separate 
the  apparently  lean  and  barren  material  from  the  high-grade 
ore.  In  the  past,  this  was  done  altogether  by  hand,  and  even 
now,  when  the  amount  of  ore  handled  is  small  and  the  labor 
cost  is  low,  the  " cobbing"  is  performed  by  men  breaking  the 
ore  into  small  pieces  and  throwing  the  lean  ore  and  rock  into  a 
waste  pile.  In  modern  iron  mining,  however,  the  ore  is  broken 
by  crushers  and  rollers,  after  which  the  broken-up  material  is 
fed  to  moving  belts  which  pass  before  the  men  who  pick  out  the 
visibly  lean  material  and  throw  it  away  while  the  balance  of 
the  ore  is  conveyed  to  bins  or  storage  piles. 


IRON  ORE  29 

Washing.  —  Washing  is  another  important  form  of  ore  con- 
centration. It  is  employed  in  order  to  separate  excessive  amounts 
of  clay,  sand,  or  gravel  from  the  ore.  It  is  especially  applied  to 
red  and  brown  hematite  ores  which  often  contain  large  quan- 
tities of  such  matter.  Red  hematite,  particularly,  is  often  mixed 
with  a  large  amount  of  clay,  and  often  from  three  to  four  tons 
of  ore  must  be  handled  before  one  ton  of  commercial  ore  is 
obtained.  Special  devices  known  as  "  log- washers "  in  which 
a  stream  of  water  flowing  in  an  opposite  direction  to  that  in 
which  the  crushed  ore  moves  are  used  for  separating  the  clay 
and  lighter  material. 

Jigging.  —  The  process  of  jigging  is  somewhat  similar  to  that 
of  washing,  and  is  used  for  removing  excessive  amounts  of  clay, 
sand,  and  rock  in  ore  which  is  too  fine  to  be  successfully  treated 
by  the  ordinary  washing  method.  In  some  cases,  the  fine  mate- 
rial from  the  washers  or  screens,  or  both,  is  also  fed  to  this 
second  washer  or  jig,  where  a  further  separation  of  ore  and  waste 
material  takes  place,  the  separation  depending  upon  the  fact 
that  the  iron  ore  has  a  higher  specific  gravity  than  most  of  the 
gangue  or  useless  material  with  which  it  is  mixed.  In  the 
jigging  process,  the  material  is  moved  in  water,  or  water  is 
forced  through  it.  In  this  way,  the  heavier  substances  form 
layers  on  the  bottom  while  the  lighter  materials  come  closer  to 
the  surface  and  can  be  removed.  Gates  adjusted  at  various 
heights  permit  the  ore  to  be  separated  from  the  waste  materials. 
By  treating  material  of  only  one  size  in  a  jig,  accurate  separation 
can  be  made,  but  it  is  necessary  that  the  material  is  of  reason- 
ably uniform  size  in  order  to  obtain  good  separation. 

Drying.  —  Ores  containing  an  excess  of  moisture  are  usually 
dried.  The  drying  is  done  for  two  purposes:  It  reduces  the 
freight  rate  proportionately  to  the  iron  content,  and  it  produces 
a  richer  ore  for  the  blast  furnace.  For  example,  an  ore  contain- 
ing 45  per  cent  of  iron  and  10  per  cent  of  moisture  will,  when 
thoroughly  dry,  contain  50  per  cent  of  iron,  by  weight. 

Roasting.  —  Roasting  is  used  to  remove  excessive  moisture 
from  damp  ores  and,  especially,  to  remove  combined  moisture 
from  hydrated  ores,  such  as  brown  hematites,  which  contain 


3° 


IRON  AND   STEEL 


water  combined  mineralogically  with  the  iron  oxide.  Roasting 
is  also  employed  for  driving  off  the  carbonic  acid  from  carbonate 
iron  ores  and  to  reduce  the  percentage  of  sulphur  in  sulphur- 
carrying  ores.  For  hematite  ores,  roasting  is  also  used  to  aid 
in  separating  clay,  sand,  and  rock  from  the  ore  itself,  and  in 
some  cases  it  is  employed  to  convert  non-magnetic  iron  oxides 
into  magnetic  ore.  The  ore  and  fuel  are  charged  in  the  roasting 
kilns,  generally  in  layers,  from  the  top,  and  the  roasted  ore  is 
removed  from  the  bottom  and  screened.  Coal,  coke,  or  gas 
may  be  used  as  a  fuel,  gas  being  the  most  advantageous,  especially 
when  blast-furnace  or  a  similar  gas  may  be  used. 

The  most  essential  point  in  roasting  is  an  abundant  supply  of 
fresh  air;  heat  alone  will  only  partly  remove  the  sulphur.  Too 
high  a  temperature,  however,  may  cause  the  ore  to  fuse  and  sinter, 
and  prevent  further  removal  of  the  sulphur.  High  sulphur  ores, 
waste  from  sulphuric-acid  factories,  etc.,  are  usually  heated  in 
" mechanical"  furnaces  in  which  motion  is  imparted  to  the  ore 
so  as  to  insure  an  even  treatment  throughout  the  mass. 

Most  of  the  kilns  in  general  use  are  of  the  Gjers  and  Grittinger 
types.  Both  of  these  kilns  have  riveted  steel-plate  shelves, 
lined  with  firebrick,  and  are  provided  with  a  cone-shaped  bot- 
tom for  the  discharge  of  the  roasted  ore.  The  Gjers  kiln  varies 
from  10  to  12  feet  in  diameter  and  from  12  to  30  feet  in  height. 
Some  of  these  kilns  are  provided  with  hoods  and  chimneys  for 
withdrawing  the  vapors.  The  ore  is  under  treatment  from  two 
to  ten  days,  and  the  furnaces  have  a  fuel  consumption  of  from 
50  to  100  pounds  per  ton  of  ore.  Coke,  coke  breeze,  or  anthra- 
cite is  the  fuel  used. 

When  producer  or  blast-furnace  gas  is  burned,  the  Davis- 
Colby  kiln  is  extensively  used.  In  this  furnace,  the  ore  is 
dumped  into  an  annular  chamber  and  is  roasted  by  gases  enter- 
ing from  a  separate  combustion  chamber. 

Transforming  Ore  into  Magnetic  Oxide.  —  Frequently,  when  it 
is  desired  to  enrich  a  non-magnetic  ore,  the  ore  is  roasted  until 
it  reaches  the  form  of  hematite,  which  consists  of  two  parts  of 
iron  and  three  parts  of  oxygen.  While  still  hot,  the  ore  is  fed 
into  a  second  kiln,  which  is  sealed  against  the  entrance  of  out- 


IRON  ORE  31 

side  air  and  heated  in  a  " reducing  atmosphere"  (one  that  can 
take  up  oxygen  from  the  ore).  This  atmosphere  is  obtained  by 
placing  in  the  kiln,  at  the  same  time  as  the  ore,  hydrocarbons 
that  have  a  greater  affinity  for  oxygen  than  has  the  ore.  This 
treatment  converts  the  hot  ore  into  "  magnetic  oxide,"  which 
consists  of  three  parts  of  iron  and  four  parts  of  oxygen,  by 
removing  part  of  the  oxygen. 

Magnetic  Concentration.  —  As  magnetic  ore  is  richer  than 
non-magnetic  ore,  magnetic  separation  is  used  for  separating 
the  strongly  magnetic  ore  from  that  which  is  non-magnetic,  so 
as  to  obtain  a  richer  ore.  The  process  consists  chiefly  in  using 
magnets  for  attracting  the  magnetic  ore.  By  this  process,  ores 
too  lean  to  be  used  directly  may  be  changed  into  ores  that  carry 
from  60  to  65  per  cent  of  iron.  Furthermore,  impurities  of 
phosphorus  and  titanium  are  frequently  present  in  the  gangue 
materials  of  magnetite,  and  are  either  greatly  reduced  or  some- 
times almost  eliminated.  It  is  also  claimed  that  larger  per- 
centages of  the  sulphur  content  of  magnetic  ores  containing 
pyrite  or  iron  sulphide  are  removed  by  magnetic  concentration 
than  by  roasting.  A  magnetic  separating  machine  must  be 
supplied  with  only  one  size  of  ore  at  a  time,  because  a  magnet 
that  is  strong  enough  to  attract  large  pieces  of  rich  ore  will  also 
be  strong  enough  to  attract  small  pieces  of  a  lean  ore,  and,  again, 
a  magnet  which  is  so  weak  that  it  can  only  separate  small  pieces 
of  good  ore  from  similar  pieces  of  lean  ore  would  not  be  able  to 
carry  heavy  pieces  of  rich  ore,  and  these  would  then  be  rejected 
by  the  machine  at  a  considerable  loss.  As  a  rule,  the  ore  is 
crushed  rather  fine  before  passing  through  the  magnetic  sepa- 
rating machines,  and  the  magnetic  concentrates  are,  therefore, 
too  finely  divided  for  furnace  use  and  must  afterwards  be  formed 
into  lumps  or  briquets  by  the  agglomeration  method. 

In  one  plant,  where  the  ore  is  concentrated  by  the  "dry" 
magnetic  process,  the  ore  passes  from  the  crushers  to  screens 
with  two-inch  holes,  the  coarse  material  returning  to  the  crushers 
while  the  fine  is  passed  to  the  magnetic  cobbers,  which  pick  out 
the  richer  part  of  the  ore.  The  tailings  are  crushed  to  pass 
through  a  screen  with  one-inch  holes,  and  are  again  passed 


32  IRON  AND   STEEL 

through  the  cobbers.  As  the  tailings  from  this  second  separa- 
tion are  again  crushed  and  passed  through  the  cobbers,  three 
products  —  heads,  middlings,  and  tails  —  are  produced. 

In  one  plant  using  the  "wet"  separation  method,  the  ore  is 
reduced  to  lumps  f  inch  or  less  in  diameter,  and  is  then  carried 
by  water  to  a  battery  of  mills  that  thoroughly  pulverize  it.  It 
is  then  passed  through  the  magnetic  separator,  which  takes  the 
finely  divided  magnetites  from  the  water  and  deposits  them  in 
settling  tanks  in  which  they  are  partly  dried.  The  tailings  pass 
off  as  sludge.  Successful  magnetic  concentration  depends  upon 
the  continuous  operation  of  the  concentration  plant,  the  feeding 
of  but  one  size  of  ore  to  the  magnetic  separating  machine,  the 
arrangement  of  the  plant  for  rapid  and  thorough  inspection, 
removing  as  soon  as  possible  all  lean  material,  passing  through 
the  drier  only  the  material  that  must  be  dried,  and  preventing 
all  fine  material  from  passing  through  the  rolls. 

Agglomeration.  —  As  fine  ores  are  difficult  to  handle  and 
cause  irregular  working  of  the  blast  furnace,  they  are  formed 
into  lumps,  or  small  masses,  by  the  various  processes  included 
under  the  heading  "  agglomeration."  In  addition  to  the  irregu- 
lar working  of  the  furnace  caused  by  the  fine  ore,  it  is  also  ob- 
jectionable because  a  considerable  amount  of  it  is  blown  out  by 
the  air  pressure  as  flue-dust,  causing  a  loss  of  iron  and  a  tendency 
to  congestion  in  the  flues.  The  finely  divided  material  may  be 
formed  into  lumps  by  briquetting,  nodulizing,  or  sintering. 

Bfiquetting.  —  Briquetting  is  one  of  the  earlier  methods  which 
consists  simply  in  mixing  the  ore  with  some  binding  material 
and  then  molding  the  mass  into  the  form  of  bricks,  or  briquets,  of 
suitable  size.  The  binding  material  must  be  of  such  a  character 
that  it  will  be  neutral  in  the  blast  furnace.  Among  the  binders 
used  are  various  clays,  water-glass,  tar,  etc.  The  bricks  are 
generally,  although  not  always,  dried  in  a  suitable  kiln.  An 
ideal  briquet  should  withstand  the  influence  of  water  and  heat 
without  disintegrating  and  should  be  able  to  resist  pressure, 
stand  severe  handling,  and  have  a  certain  porosity. 

Nodulizing.  —  The  nodulizing  process  consists  in  transform- 
ing fine  ore  into  larger  lumps  by  feeding  it  into  large  iron  cyl- 


IRON  ORE  33 

inders  or  rotary  kilns,  like  those  used  in  cement-burning,  in 
which  the  ore  is  heated  until  the  fine  material  congeals  into  firm 
and  porous  lumps  or  nodules.  No  binder  is  used  in  this  process. 
The  rotary  kilns  used  are  inclined  iron  cylinders  of  from  7  to  10 
feet  in  diameter  and  from  80  to  120  feet  long.  They  are  lined 
with  firebrick  and  revolved  upon  rollers  at  from  one  to  two 
revolutions  per  minute.  The  concentrate  or  fine  ore,  sometimes 
mixed  with  tar,  is  charged  at  the  higher  end,  and,  after  being 
sintered,  is  discharged  from  the  lower  end  in  the  form  of  nodules. 
These  may  vary  in  size  from  about  3  inches  in  diameter  down 
to  lumps  that  will  pass  through  a  i2-mesh  screen.  As  the  fuel 
is  fed  at  the  lower  end  of  the  cylinder,  the  highest  temperature 
of  the  furnace  (from  2350  to  2550  degrees  F.)  is  maintained 
about  15  feet  from  the  lower  end.  The  fuel  may  consist  of  pul- 
verized coal,  gas,  or  tar,  but  the  coal  must  be  dry  before  it  is 
pulverized,  and  should  contain  at  least  25  per  cent  of  volatile 
matter.  These  kilns  have  a  capacity  of  about  100  tons  per 
day.  They  must  be  cleaned  about  every  ten  days,  because  of 
the  rings  of  sintered  ore  that  are  formed  about  15  feet  from  the 
lower  end.  In  some  cases,  these  kilns  have  reduced  the  sulphur 
content  of  the  ore  from  i  to  0.03  or  0.05  per  cent. 

Sintering.  —  The  sintering  process  is  also  used  for  producing 
lumps  irom  the  fine  ore  by  means  of  heat  without  a  binder,  the 
same  as  the  nodulizing  process,  but  the  method  of  producing 
the  heat  is  different.  In  this  process,  the  fine  ore  is  mixed  with 
fine  coal  or  coke  breeze  and  fed  upon  a  movable  bed  or  table  at 
a  rate  that  will  give  the  best  results  for  the  ore  undergoing 
treatment.  The  fuel  in  the  bed  is  then  ignited  by  a  gas  flame 
and  burned  with  a  forced  draft;  by  means  of  the  heat  thus  pro- 
duced, the  fine  ore  is  sintered  into  a  slab,  when  the  draft  is  dis- 
continued. The  slabs  are  then  broken  into  sizes  convenient  to 
handle.  The  high  temperatures  also  drive  off  the  hygroscopic 
moisture,  sulphur,  and  combined  water. 


CHAPTER   III 
PIG  IRON  AND  ITS  PRODUCTION  IN  THE  BLAST  FURNACE 

PIG  iron  is  the  product  obtained  by  smelting  iron  ore  in  a 
blast  furnace.  A  mixture  of  ore,  fuel,  and  flux  is  charged  into 
the  top  of  the  furnace.  A  chemical  reaction  takes  place  by 
means  of  which  the  ore  is  reduced,  and  molten  iron  collects  in, 
and  is  drawn  from,  the  bottom  of  the  furnace,  after  which  the 
metal  is  cast  into  bars  of  convenient  size,  called  "pigs,"  except 
when  it  is  to  be  converted  directly  into  steel.  It  is  thus  seen 
that  pig  iron  is  obtained  directly  from  the  iron  ore;  it  is  the  raw 
material  used  in  the  production  of  all  other  kinds  of  iron  and 
steel.  Pig  iron  is  remelted  in  a  cupola  furnace  for  making  ordi- 
nary iron  castings,  and  is  converted  into  wrought  iron  by  the 
puddling  process,  and  into  steel  of  cliff erent  kinds  by  the  Bes- 
semer or  open-hearth  processes.  It  is  also  the  raw  material  for 
crucible  steel,  except  that,  in  this  case,  two  processes  are  re- 
quired; first  the  making  of  wrought  iron  from  the  pig  iron,  and 
then  the  making  of  crucible  steel  from  the  wrought  iron  Pig 
iron  contains  about  93  per  cent  of  iron  and  from  3  to  5  per  cent 
of  carbon,  the  remainder  being  made  up  of  varying  percentages 
of  sulphur,  phosphorus,  silicon,  and  manganese.  The  terms 
"pig"  and  "pig  iron"  are  derived  from  the  original  method  in 
which  the  bars  of  this  iron  are  cast  in  depressions  in  the  sand 
floor  about  the  blast  furnace.  A  runner  or  feeder,  known  as 
the  "sow,"  is  provided,  and  this,  in  turn,  is  connected  with  the 
depressions  and  molds  for  the  pig-iron  bars,  which  are  at  right 
angles  to  it.  The  runner  is  filled  with  metal,  and  from  the  run- 
ner, the  molds  for  the  pig-iron  bars  are  filled.  This  runner  and 
the  numerous  smaller  molds  were  supposed  to  resemble  a  litter 
of  sucking  pigs;  hence  the  name  "pig  iron."  In  modern  prac- 
tice, there  are  various  other  ways  for  casting  pigs.  Those  cast 
in  the  manner  described  are  known  as  "sand-cast  pig,"  while 
those  made  in  metal  molds  or  chills  are  known  as  "chill-cast 

34 


PIG  IRON 


35 


pig,"  and  those  produced  in  special  casting  machines,  as  " ma- 
chine-cast pig." 

The  Blast  Furnace.  —  The  modern  blast  furnace  is  a  develop- 
ment of  the  furnace  that  originated  in  the  Rhine  provinces  in 


Fig.  I.   A  Blast  Furnace 

the  early  part  of  the  fourteenth  century.  Aside  from  experi- 
menting with  various  fuels  and  finally  adopting  coke  as  the 
principal  fuel,  the  only  changes  made  in  the  furnace  for  about 
four  centuries  were  in  height;  as  the  height  was  raised,  the  out- 
put and  economical  working  were  increased.  In  1829,  however, 
J.  B.  Neilson  greatly  reduced  the  fuel  consumption  and  in- 
creased the  output  by  warming  the  blast.  In  recent  years, 


36  IRON  AND   STEEL 

James  Gayley  increased  the  heat  produced  in  the  melting  zone, 
while  decreasing  the  amount  of  fuel  required,  by  drying  the  air 
of  the  blast. 

While  operating  on  the  same  principle  as  the  early  furnace, 
the  modern  blast  furnace  differs  greatly  from  it.  Originally,  the 
furnace  was  built  of  solid  masonry.  Later  it  was  an  iron-en- 
cased, double  brick-wall  structure;  the  outer  wall  was  made  of 
common  brick,  and  the  inner  wall  of  firebrick.  The  narrow 
space  left  between  the  walls,  to  allow  for  contraction  and 
expansion,  as  well  as  to  prevent  the  loss  of  heat  through  radia- 
tion, was  filled  with  ashes.  As  the  loss  of  heat  through  radia- 
tion has  been  found  to  be  unobjectionable,  and,  in  fact,  lessens 
the  necessity  for  as  frequent  repairs,  the  modern,  steel-encased, 
firebrick,  single-wall  structure  has  been  evolved.  The  furnace 
is,  however,  only  one  of  the  necessary  parts  of  the  plant.  Its 
successful  operation  requires  hot-blast  stoves  and  blowing  en- 
gines for  the  blast,  and  other  auxiliary  equipment.  An  exterior 
view  of  a  modern  blast  furnace  is  shown  in  Fig.  i. 

Arrangement  of  a  Blast  Furnace.  —  The  blast  furnace,  as 
shown  in  Fig.  2  equipped  with  a  mechanical  hoist  for  carrying 
the  charge  to  the  top  of  the  furnace,  consists  mainly  of  four 
parts:  The  hearth  A,  the  bosh  B,  the  shaft  C,  and  the  throat  D. 
The  throat  and  top  part  of  the  shaft  form  the  " reduction"  or 
" oxidation"  zone;  the  rest  of  the  shaft  forms  the  "heating" 
zone;  at  the  junction  of  the  shaft  and  the  bosh  is  the  "melting" 
zone;  between  this  and  the  tuyeres  (indicated  immediately 
beneath  the  "B"  zone)  is  the  zone  of  " carburization " ;  and  the 
lower  part  of  the  hearth  or  the  part  of  the  furnace  below  the 
tuyeres  is  the  "collecting"  zone.  Sometimes  the  bottom  of 
the  shaft  has  parallel  sides,  but,  in  most  cases,  the  diameter 
gradually  increases  from  the  throat  to  the  top  of  the  bosh,  and 
then  gradually  decreases  to  the  top  of  the  hearth,  the  sides  of 
which  are  generally  parallel,  except  for  a  foot  or  so  from  the 
bottom.  This  constantly  increasing  diameter  of  the  shaft  aids 
the  downward  passage  of  the  charge  and  also  provides  room  for 
its  expansion;  while  the  sloping  sides  of  the  bosh  support  the 
charge  and  lessen  the  pressure  on  the  molten  metal  in  the  bottom 


PIG   IRON 


37 


of  the  hearth.  The  reduction  of  this  pressure  lessens  the  pres- 
sure at  the  tap  hole  and  permits  the  metal  to  be  under  better 
control  with  less  liability  of  cutting  the  breast  as  the  metal 


Fig.  2.     Sectional  View  of  Blast  Furnace 

flows  out  to  the  runner.  This  reduction  in  the  diameter  of  the 
bosh  also  makes  it  easier  for  the  blast  to  reach  the  center  of  the 
charge. 

Size  of  Blast  Furnace  and  Angles  of  Walls.  —  A  large  furnace 
is  more  economical  to  build  and  maintain  per  unit  of  product 


38  IRON  AND  STEEL 

than  a  small  one,  but  a  furnace  will  not  operate  satisfactorily 
if  more  than  12  J  feet  wide  at  the  tuyeres.  In  furnaces  of  the 
Pittsburg  type,  the  bosh  flares  outwards,  for  12  feet  from  the 
tuyeres,  at  an  angle  of  from  73  to  76  degrees  with  the  horizontal. 
The  charge  will  slide  easily  over  the  sides  at  this  angle,  while  a 
greater  angle  will  cause  irregular  working.  The  irregular  work- 
ing is  due  to  the  fact  that  the  steeper  sides  unduly  favor  the 
passage  of  the  blast  along  the  walls,  instead  of  up  and  through 
the  charge,  with  the  result  that  the  outside  of  the  column  of  the 
charge  is  deoxidized  more  rapidly  than  the  core,  which  arrives 
at  the  bottom  in  an  improper  condition.  The  walls  of  the  shaft 
make  an  angle  of  from  3  to  8  degrees  with  the  vertical.  A 
greater  angle  leads  to  irregular  working  of  the  furnace.  In 
order- that  the  charge  may  be  evenly  distributed,  the  throat  is 
made  rather  narrow  at  the  top.  If  it  is  made  too  narrow,  the 
escaping  gases  will  move  so  rapidly  through  it  as  to  carry  away 
much  of  the  fine  ore;  besides,  the  throttling  will  give  the  blowing 
engines  more  work  to  do. 

It  has  been  found  that  90  feet  is  the  most  economical  height 
of  furnace,  and  that  the  best  run  is  a  daily  output  of  400  tons  of 
iron.  This  output  requires  the  charging  into  the  furnace  of 
800  tons  of  ore,  400  tons  of  coke,  and  100  tons  of  limestone, 
each  twenty-four  hours.  During  the  first  four  months  of  1914, 
the  average  daily  output  of  the  blast  furnaces  in  the  United 
States  was  105,814  tons.  The  approximate  average  annual  pro- 
duction per  furnace,  in  the  United  States,  is  90,000  tons;  in 
Germany,  50,000  tons;  and  in  England,  35,000  tons.  In  the 
United  States,  about  i  ton  of  coke  is  required  for  each  ton  of 
iron  produced;  in  Germany,  i.i  ton  is  required;  and  in  England, 
1.15  ton. 

Construction  of  Blast  Furnace.  —  When  a  7o-foot  furnace 
with  a  hearth  9  feet  in  diameter  is  completely  charged,  the  base 
must  support  300  tons  besides  the  weight  of  the  furnace.  It  is, 
therefore,  most  essential  for  the  blast  furnace  to  have  an  espe- 
cially good  foundation.  This  is  often  made  of  firebrick  about 
five  feet  thick,  placed  upon  a  stone  or  concrete  base  of  about  the 
same  thickness,  although  the  exact  size  varies  in  each  case.  The 


PIG  IRON 


39 


furnace  is  a  firebrick  shell  of  varying  thickness.  In  the  usual 
construction,  the  bosh  walls  are  from  18  to  20  inches  thick, 
while  the  walls  of  the  shaft  may  be  36  inches  thick.  The  shaft 
and  throat  are  encased  in  a  steel-plate  shell,  which,  with  part 
of  the  shaft  wall,  is  built  upon  an  iron  ring  that  is  supported  by 
cast-iron  columns.  A  3-  or  4-inch  space  between  the  firebrick 
wall  and  the  steel  shell  permits  of  their  contraction  and  expan- 
sion. This  space  is  filled  with  an  easily  compressible  substance, 
usually  slag  granulated  by  being  run,  while  molten,  into  water. 
The  bosh,  however,  is  not  encased  by  a  shell.  The  brickwork 
is  supported  by  wrought-iron  bands,  6  inches  wide  and  i  inch 
thick,  placed  every  two  feet  in  height.  The  lower  part  of  the 
hearth  is  also  supported  by  a  thick  iron  band.  Often  this  part 
is  surrounded  by  a  trough  about  8  inches  wide  and  3^  feet  deep, 
which  contains  water  that  is  sprayed  against  the  iron  plate  from 
a  pipe  that  encircles  the  hearth.  The  depth  of  water  in  this 
trough  is  regulated  by  valves. 

The  comparatively  thin  walls  of  the  bosh  are  made  possible 
only  by  the  insertion  in  them  of  bronze  or  copper  boxes  through 
which  water  is  constantly  passing.  The  boxes  are  placed  in 
rows  that  encircle  the  bosh.  These  rows  are  usually  located 
about  two  feet  apart  between  the  tuyeres  and  the  top  of  the 
bosh.  Sometimes  one  or  two  rows  are  placed  below  the  tuyeres, 
and  two  or  three  above  the  joint  of  the  bosh  and  the  shaft. 
When  the  furnace  is  to  be  driven  hard,  sometimes  the  bosh  is 
built  of  cast-iron  cooling  blocks  that  have  a  very  thin  lining  of 
refractory  brickwork;  these  blocks  are  kept  from  melting  or 
burning  by  causing  water  to  circulate  through  them. 

Furnace  Top.  —  In  early  furnaces,  the  top  of  the  furnace  was 
open,  but  now  it  is  closed  by  a  bell  E,  Fig.  2,  in  order  that  the 
heat  of  combustion  and  the  gases  used  for  heating  the  blast  may 
be  retained.  The  bell  may  be  moved  vertically  to  admit  the 
charge  into  the  furnace.  Above  the  bell  is  a  hopper  F  in  which 
the  charge  is  placed  before  it  is  dumped  into  the  furnace.  In 
modern  equipments,  this  hopper  is  charged  by  skips  G  traveling 
on  a  hoist  H.  These  skips  dump  automatically  and  are  usually 
filled  direct  from  the  bins  or  cars.  As  the  hopper  is  filled,  the 


40  IRON  AND   STEEL 

bell  is  operated  by  means  of  steam  or  blast  pressure.  Modern 
furnaces,  generally,  have  a  double-bell  arrangement  so  that  no 
gases  can  escape  when  the  charge  enters  the  furnace,  as  is  the 
case  when  the  single  bell  is  used.  The  bell  must  be  hung  true, 
because,  if  one  side  should  swing  lower  than  the  other  when  the 
charge  is  admitted  to  the  furnace,  the  charge  will  lodge  unevenly, 
and  will  have  a  tendency  to  cause  irregular  working.  The 
distribution  and  position  of  the  coarse  and  fine  material  in  the 
charge,  and  also  the  formation  of  irregularities  in  the  mounds 
that  a  charge  may  assume  after  being  dropped  by  a  bell,  are 
dependent  upon  the  angle  and  diameter  of  the  bell  and  hopper, 
compared  with  the  diameter  of  the  furnace  at  its  throat.  A 
comparatively  small  bell  causes  the  coarse  and  the  fine  stock  to 
descend  at  about  the  same  rate. 

Tuyeres.  —  The  complete  oxidation  of  the  charge  requires 
that  the  air  necessary  be  furnished  at  a  pressure  of  from  6  to  24 
pounds.  This  air  is  admitted  to  the  furnace  through  the  tuyeres 
shown  at  the  upper  end  of  hearth  A,  Fig.  2.  The  tuyeres  are 
made  of  a  copper  alloy  that  closely  resembles  bronze,  to  which 
it  has  been  found  that  molten  iron  has  the  least  tendency  to 
stick.  The  tuyeres  are  placed  about  6  feet  above  the  bottom 
of  the  hearth  and  project  from  6  to  10  inches  beyond  the  furnace 
lining,  in  order  that  the  blast  may  reach  the  center  of  the  charge 
and  also  to  protect  the  lining  from  the  intense  heat  developed 
at  their  ends.  To  prevent  their  melting  or  burning,  the  tuyeres 
are  placed  within  bronze  boxes  through  which  water  circulates; 
as  a  rule,  the  tuyeres  may  be  easily  removed  from  the  boxes  for 
repairs  or  renewal.  The  tuyeres  receive  air  from  a  ''bustle 
pipe,"  which  is  a  steel  pipe  with  a  g-inch  lining  of  firebrick  that 
is  placed  from  10  to  15  feet  above  the  floor.  The  bustle  pipe 
and  tuyeres  are  usually  connected  by  a  brick-lined  "  tuyere 
stock,"  or  " gooseneck,"  and  a  blowpipe  that  fits  into  the  tuyeres. 
These  parts  are  so  connected  that  they  may  be  easily  taken 
apart  for  repairs.  An  opening  in  the  lower  end  of  the  tuyere 
stock  permits  the  tuyeres  to  be  cleaned  of  obstructions  by 
pushing  a  bar  through  it,  and  a  hole,  closed  with  blue  glass,  in 
this  end,  permits  the  working  of  the  furnace  to  be  watched. 


PIG  IRON  41 

The  Blast.  —  When  charcoal  iron  is  being  made,  a  cold  blast 
is  used;  but  when  coal  or  coke  is  the  fuel,  a  hot  blast  must  be 
employed.  When  Neilson  discovered  the  advantages  of  the  hot 
blast,  the  temperature  of  the  air  was  raised  by  a  so-called  "  hot- 
blast  stove"  in  stages  of  100  degrees  F.  The  experiments 
showed  that  much  better  results  were  obtained  with  each  100- 
degree  rise  in  the  temperature  until  600  degrees  F.  was  reached, 
after  which  there  was  little  improvement  until  800  degrees  F. 
was  obtained;  but,  in  the  rise  from  1000  to  1200  degrees  F.,  the 
results  were  very  much  greater  than  at  any  other  increase  of 
200  degrees.  Many  furnace  men  claim,  however,  that  any  in- 
crease in  the  temperature  of  the  blast  above  1200  degrees  F.  is 
more  injurious  to  the  stock  than  beneficial  to  the  working  of 
the  furnace;  but  temperatures  of  from  1500  to  1600  degrees  F. 
are  sometimes  used  when  the  furnace  is  chilled,  and  in  other 
emergencies. 

As  the  blast  enters  the  furnace,  the  oxygen  it  contains  com- 
bines with  the  carbon  of  the  fuel  and  produces  carbon  dioxide, 
C02,  which  is  necessary  to  liquidize  the  metal  and  slag.  As 
the  gas  passes  upwards,  it  combines  with  more  carbon  until  the 
reducing  agent,  carbon  monoxide,  CO,  is  formed.  The  amount 
of  air  that  must  pass  through  the  furnace  for  the  smelting  of 
the  ore  is  much  greater  than  the  combined  weight  of  the  fuel, 
ore,  and  flux  of  the  charge.  The  amount  of  heat  necessary  to 
decompose  this  air  depends  upon  the  amount  of  moisture  it 
contains.  In  summer,  the  humidity  of  the  air  is  so  great  that 
furnaces  do  not  produce  as  much  iron  as  in  the  months  when 
the  air  is  generally  drier.  Heating  the  blast  does  not  drive  of! 
this  moisture;  it  simply  changes  it  into  a  vapor  that  passes  into 
the  furnace  as  steam.  It  has  been  estimated  that  frequently, 
during  the  summer  months,  twenty  tons  of  water  are  thus  trans- 
ferred into  the  furnace  in  one  day. 

By  means  of  the  Gayley  process,  the  moisture  is  removed 
from  the  air  by  being  passed  over  coils  that  reduce  its  tempera- 
ture to  25  or  30  degrees  F.,  and  the  moisture  is  then  deposited 
on  the  coils  in  the  form  of  snow  or  ice.  The  air,  which  contains 
about  from  1.5  to  2  grains  of  moisture  per  cubic  foot,  then  passes 


42  IRON  AND  STEEL 

through  the  hot-blast  stove  in  the  usual  manner.  The  removal 
of  4  grains  of  moisture  is  equivalent  to  reducing  the  amount  of 
coke  required  in  the  charge  about  60  pounds  for  each  ton  of  pig 
iron  produced.  In  some  cases,  the  use  of  this  process  has  re- 
duced the  fuel  consumption  20  per  cent  while  increasing  the 
output  the  same  amount;  besides,  the  working  of  the  furnace  is 
improved,  because  the  amount  of  moisture  does  not  vary.  The 
rate  of  blowing  is,  perhaps,  the  factor  that  affects  the  output 
the  most;  for,  as  the  volume  of  air  is  increased,  the  consumption 
of  the  coke  and  the  smelting  of  the  ore  are  increased.  It  is, 


Fig.  3.     Blowing  Engines  for  Blast  Furnaces 

therefore,  important  to  install  good  blowing  equipment.  Fig.  3 
shows  a  view  in  the  blowing  engine  room  of  the  blast  furnace 
department  of  the  Carnegie  Steel  Co.  (Clairton  Works). 

Iron  Blast  Stoves.  —  When  Neilson  introduced  the  warm 
blast,  he  passed  the  air  through  pipes  set  in  a  circular  furnace 
and  heated  by  a  coal  fire.  Later,  these  pipes  were  placed  upon 
the  top  of  the  furnace  and  heated  by  the  waste  furnace  gases; 
but,  when  the  closed  furnace  top  was  adopted,  the  gases  were 
passed  through  "stoves"  to  heat  the  blast.  At  first,  the  stoves 
consisted  of  a  number  of  pipes  around  which  the  burning  gases 


PIG  IRON  43 

passed.  Iron  stoves,  however,  are  now  being  displaced  by  brick 
stoves,  because  the  iron  stoves  cannot  be  economically  heated 
above  900  degrees  F.,  or  they  will  burn  out  rapidly;  besides, 
fluctuations  in  temperature  cause  the  pipes  to  crack,  owing  to 
expansion  and  contraction,  while  the  friction  produced  by  the 
air  passing  through  the  long  tortuous  passages  throws  consid- 
erable extra  work  on  the  engines.  Although  cheaper  to  install 
than  the  brick  stoves,  the  cost  of  maintenance  is  so  much  greater 
that  (with  the  reduced  cost  of  smelting,  because  of  the  higher 
temperature  obtained  with  the  brick  stove)  in  one  case  a  change 
from  the  iron  to  the  brick  stove  reduced  the  cost  of  producing 
pig  iron  30  cents  a  ton.  If  the  furnace  "goes  out  of  blast,"  for 
any  reason,  a  wood  or  coal  fire  must  be  built  in  the  iron  stove, 
otherwise  the  stove  may  become  so  cold  that,  when  the  gas 
again  enters,  it  will  not  ignite  but,  instead  of  burning  quietly, 
may  explode.  Not  only  must  the  stove  be  hot  when  the  gas 
enters  it,  but  there  should  be  a  flame  to  insure  the  ignition  of 
the  gas.  Some  furnace  men  throw  a  lump  of  coal  or  a  piece  of 
dry  wood  into  the  stove  whenever  the  furnace  is  shut  down. 

Brick  Blast  Stoves.  —  In  the  three-pass,  center-combustion, 
regenerative,  brick  blast  stove,  the  gas  from  the  blast  furnace 
enters  at  the  bottom  and  immediately  ignites,  as  the  air  neces- 
sary for  its  combustion  is  admitted  at  the  same  time.  The 
burning  gas  then  passes  up  a  large  center  chamber  until  it  is 
deflected  by  the  dome  into  the  narrow  flues  surrounding  this 
central  space;  then,  passing  through  large  flues  at  the  bottom, 
it  goes  up  flues  along  the  outside  walls  and  enters  the  chimney. 
After  the  brickwork  is  heated  to  the  incandescent  state,  the  gas 
is  shut  off  and  the  cold  blast  from  the  main  is  admitted  into 
the  lower  part  of  the  chimney.  Passing  downwards,  the  air  is 
deflected  by  the  dome  into  the  outside  flues,  whence  it  passes 
through  the  small  flues  and  the  large  central  flue  into  the  hot- 
blast  pipe.  As  soon  as  the  passage  of  the  cold  air  has  cooled 
the  brickwork  so  that  it  will  not  raise  the  blast  to  the  desired 
temperature,  the  cold  air  is  shut  off  and  the  furnace  gas  admitted 
once  more.  As  a  rule,  the  furnace  is  "on  gas"  for  about  three 
hours  and  "on  wind"  about  one. 


44  IRON  AND   STEEL 

As  the  work  of  the  stove  is  intermittent,  three  or  four  stoves 
are  usually  provided  for  each  furnace.  In  a  plant  of  two  fur- 
naces, seven  stoves  are  sometimes  built,  the  middle  one  being 
arranged  so  that  it  can  be  used  by  either  furnace.  Three 
stoves  are  generally  on  gas,  while  one  is  on  wind.  The  stoves 
must  be  cleaned  often  of  the  caked  flue-dust,  which  rapidly  col- 
lects in  the  combustion  chamber  for  a  height  of  about  20  feet. 
As  a  rule,  the  stoves  are  built  as  closely  together  as  possible 
and  are  connected  by  pipes  and  separate  valves,  so  that  the 
cold  blast  coming  from  the  blowing  "tubs,"  and  the  hot  blast 
leading  from  the  four  stoves,  come  from,  and  lead  into,  one 
main  pipe.  The  "downcomer"  -that  is,  the  duct  for  the 
blast  furnace  gas  —  and  the  pipes  carrying  the  hot  blast  to  the 
furnace  are  either  coated  with  asbestos  or  are  brick-lined,  to 
protect  them  and  prevent  loss  of  heat  through  radiation.  Brick 
blast  stoves  are  usually  about  100  feet  high  and  20  feet  in  diam- 
eter. When  the  air  and  gas  pass  through  the  stove  only  once, 
the  stove  is  termed  a  " single-pass "  stove;  in  a  " three-pass" 
stove,  the  air  and  gas  are  caused  to  pass  through  three  times. 

Charging  the  Furnace.  —  In  early  furnaces,  the  furnace  was 
charged  by  dumping  into  it  the  proper  amount  of  fuel,  flux,  and 
ore  from  hand  barrows.  To  facilitate  this  work,  the  furnace 
was  often  placed  alongside  a  bank  so  that  the  top  could  easily 
be  reached  by  means  of  platforms.  As  the  height  of  the  furnace 
increased,  the  barrows  were  raised  to  the  top  of  the  furnace  by 
elevators.  This  method  made  necessary  the  employment  of 
two  gangs  of  men;  one  on  the  ground,  loading  the  barrows  and 
wheeling  them  to  the  elevators,  and  the  other  at  the  top  taking 
the  loaded  barrows  from  the  elevators  and  dumping  them  into 
the  furnace.  The  increased  size  and  output  of  blast  furnaces 
later  required  mechanical  charging  methods  to  be  adopted. 

In  most  modern  plants,  the  charge  is  placed  on  skips  that  are 
drawn  up  inclined  planes  (sometimes  perpendicular  shafts  are 
used)  and  automatically  dumped.  By  this  method,  no  men 
are  required  at  the  furnace  top,  except  when  necessary  to  oil 
or  repair  the  machinery.  In  the  larger  plants,  two  skips  are 
used,  running  on  parallel  tracks;  one  skip  goes  up  with  a  load 


PIG  IRON  45 

as  the  other  is  coming  down.  It  is  necessary  that  the  charge 
be  evenly  distributed  in  the  furnace.  When  the  hand  barrows 
were  emptied  into  the  furnace,  the  stock  was  so  dumped  that 
each  kind  of  material  occupied  a  different  horizontal  position 
in  each  succeeding  charge,  or,  in  other  words,  the  position  of 
each  was  rotated  in  successive  layers.  When  mechanical  charg- 
ing was  first  used,  the  coarse  and  fine  material  separated,  with 
the  result  that  each  was  dumped  on  opposite  sides  of  the  fur- 
nace. The  furnace  then  worked  hotter  on  the  side  containing 
the  coarse  material  than  on  the  other,  which  caused  a  rapid 
erosion  of  the  lining  on  that  side;  while  the  fine  material  on  the 
opposite  side  of  the  stack  caused  an  uneven  descent  of  the 
charge  and  irregular  working  of  the  furnace.  While  several 
plans  have  been  tried  for  the  elimination  of  these  troubles,  one 
of  the  most  common  devices  is  a  modification  of  the  double 
bell. 

The  relative  proportions  of  the  charge  vary  with  the  nature 
of  the  ore,  the  fuel,  and  the  pig  iron  to  be  produced.  When 
red  hematite  is  used,  the  production  of  one  ton  of  pig  iron  re- 
quires the  charge  to  consist  of  2  tons  of  ore,  i  ton  of  fuel,  and  0.4 
ton  of  flux;  while  the  use  of  "clay  iron-stone"  requires  the 
charge  to  consist  of  2.4  tons  of  ore,  i  ton  of  fuel,  and  0.6  ton  of 
flux. 

Action  of  Furnace.  —  As  the  charge  descends,  it  is  penetrated 
by  the  gases  and  chemical  reaction  takes  place.  The  first  ma- 
terial to  be  affected  is  the  ore,  which  the  carbon  monoxide 
reduces  to  a  finely  divided  sponge  of  metallic  iron  or  to  a  mix- 
ture of  iron  and  oxides.  In  the  case  of  easily  reduced  ores,  this 
action  begins  at  a  temperature  of  400  degrees  F.,  but  it  becomes 
more  rapid  as  the  temperature  increases,  until  1200  degrees  F.  is 
reached,  when  the  action  is  completed.  Some  furnace  men  be- 
lieve that  the  action  is  finished  at  a  temperature  of  1000  de- 
grees F.  The  decomposition  of  the  flux  is  the  second  action  to 
take  place.  Limestone  is  decomposed  into  calcium  oxide  and 
carbon  dioxide,  and  dolomite  is  decomposed  into  magnesia  and 
carbon  dioxide.  This  decomposition  is  generally  thought  to 
take  place  in  the  second  30  feet  of  the  descent  when  the  tern- 


46  IRON  AND  STEEL 

perature  reaches  from  uoo  to  1600  degrees  F.  While  lime  is 
infusible  at  the  highest  temperature  of  the  blast  furnace,  the 
silica  and  alumina  of  the  ore  and  the  ash  of  the  fuel  make  the 
lime  fusible  at  the  temperature  of  the  hearth,  so  that  it  forms 
the  slag. 

The  fuel  is  not  chemically  affected  to  any  extent  until  it 
reaches  the  tuyeres.  The  only  action  that  takes  place  is  that 
its  temperature  is  gradually  raised,  the  moisture  is  expelled,  and 
a  little  of  its  carbon  is  transformed  into  carbon  dioxide.  At 
the  tuyeres,  however,  the  blast  converts  much  of  the  carbon 
into  carbon  dioxide,  which  the  excess  coke  at  once  reduces  to 
carbon  monoxide.  Some  of  the  coke  is  carried  into  the  hearth 
where  it  carburizes  the  metal.  As  the  descending  charge  reaches 
the  tuyeres,  it  is  melted;  the  molten  iron  gathers  at  the  bottom 
of  the  hearth,  and  the  slag,  being  lighter,  floats  upon  it.  As  the 
amount  'of  molten  matter  increases,  the  slag  is  drawn  off  through 
the  slag  hole,  and  the  molten  iron,  which  collects  at  the  bottom 
of  the  hearth,  is  tapped  at  regular  intervals.  As  the  charge 
settles  and  melts,  more  fuel,  flux,  and  ore  are  thrown  in  at  the 
top  in  the  order  named. 

After  the  blast  furnace  is  lighted,  it  is  kept  in  operation  until 
it  needs  repairs;  sometimes  this  period  of  operation  lasts  a  year. 

Making  the  Pigs.  —  When  enough  molten  iron  has  accumu- 
lated in  the  furnace,  it  is  drawn  out  and,  when  intended  for  pig 
iron,  allowed  to  run  into  molds  in  which  it  is  formed  into  pigs; 
or  it  is  carried  by  ladles  to  the  mixer  (see  Fig.  4),  from  which  it 
is  taken  to  the  Bessemer  converter  or  the  open-hearth  furnace, 
when  it  is  to  be  made  into  steel.  The  older  method  of  making 
pig  iron  is  to  run  the  molten  metal  into  sand  molds.  These 
molds  are  formed  by  making  a  bed  two  or  three  feet  deep  of  the 
medium  grade  of  bank  sand,  the  bed  being  made  to  slope  about 
1 8  inches  in  100  feet,  so  that  the  molten  metal  will  flow  easily 
over  it.  The  metal  leaving  the  furnace  passes  through  the 
main  runner  into  smaller  runners,  termed  "sows,"  from  which 
the  metal  flows  directly  into  the  "pigs."  These  are  generally 
semi-cylindrical  in  shape,  and  are  about  5  inches  wide  by  36 
inches  long,  and  weigh  about  100  pounds.  There  are  usually 


PIG  IRON 


47 


about  100  pigs  to  a  sow.  After  the  pigs  and  sows  have  solidified 
enough  so  that  they  will  not  u  bleed,"  they  are  covered  with 
about  J  inch  of  sand.  Then  men  wearing  shoes  with  thick 
wooden  soles  break  the  pigs  from  the  sows  by  inserting,  at  the 
point  where  they  are  joined,  pointed  ij-inch  bars.  The  sows 
are  broken  into  pieces  by  prying  them  up  from  the  molds,  or  by 
sledges.  As  soon  as  they  are  broken,  a  stream  of  water  is 
turned  upon  the  iron  to  cool  it  quickly,  so  that  it  may  be  re- 


Fig.  4.    Ladle  receiving  Molten  Metal  from  Blast  Furnace 

moved  and  the  bed  prepared  for  the  next  run  of  iron.  Usually 
two  beds  are  used,  one  being  made  ready  to  receive  the  molten 
iron  as  the  iron  in  the  other  bed  is  being  removed.  In  some 
plants,  the  pigs  and  sows  are  broken  by  being  picked  up  by  a 
crane  and  carried  to  a  pig  breaker.  Here  the  pigs  are  broken 
from  the  sows  and  then  broken  into  pieces  in  order  that  they 
may  be  graded  and  handled  more  easily. 

Pig-casting  Machines.  —  To  reduce  the  labor  cost  and  also 
to  avoid  the  work  of  breaking  the  hot  metal,  several  methods  of 


48  IRON  AND  STEEL 

using  iron  molds  have  been  tried.  One  of  the  most  widely 
adopted  is  by  means  of  a  pig-casting  machine  which  consists  of 
a  series  of  iron  molds  carried  by  an  endless  chain.  As  these 
molds  pass  a  ladle,  they  are  filled  with  the  molten  metal,  the 
speed  of  the  conveyor  being  properly  adjusted  for  this  purpose. 
One  edge  of  each  mold  overlaps  the  mold  next  to  it,  so  that  no 
metal  is  spilled.  After  passing  through  the  air  for  a  short 
distance,  the  molds  are  slowly  passed  through  a  tank  of  water, 
or,  in  some  cases,  up  an  inclined  plane  where  they  are  sprayed. 
They  are  then  dumped  into  cars  and  are  ready  for  shipment. 
As  the  empty  molds  return  to  the  pouring  end,  they  pass  over  a 
lime  vat  and  are  sprayed  with  a  milk-of-lime  wash,  which  pre- 
serves them  and  prevents  the  pigs  sticking  to  them.  This 
method  eliminates  the  work  of  making  the  molding  beds,  the 
breaking  of  the  hot  pigs,  and  all  handling  necessary  to  ship  the 
iron;  besides,  the  molds  chill  the  pigs,  making  a  harder  iron  that 
holds  more  of  the  carbon  in  the  combined  state.  As  the  iron  is 
free  from  sand,  less  time  and  fuel  are  required  to  melt  it  in  the 
foundry;  less  flux,  too,  is  required,  so  that  there  is  less  slag  to 
take  care  of,  and  a  cleaner  iron  is  poured.  The  pig  is  more  uni- 
form in  composition  because  the  iron  is  tapped  from  the  furnace 
into  a  large  ladle  in  which  it  becomes  mixed  into  a  homogeneous 
liquid,  while  the  pigs  from  the  sand  molds  are  cast  just  as  the 
iron  runs  from  the  furnace,  and  there  is  always  a  difference 
between  the  first  and  the  last  part  of  the  tap. 

The  Slag.  —  The  amount  of  slag  formed  depends  upon  the 
raw  materials.  With  Lake  Superior  ores,  about  one-half  ton  of 
slag  is  made  for  every  ton  of  pig  iron  produced.  As  the  slag, 
however,  has  only  one-third  the  specific  gravity  of  the  molten 
iron,  its  volume  is  ij  times  that  of  the  iron.  With  siliceous 
mixtures,  the  weight  of  the  slag  may  equal,  or  even  exceed,  that 
of  the  iron  produced,  so  that  at  least  two  taps  of  slag  are  made 
for  every  tap  of  iron.  Less  slag  is  formed  in  the  smelting  when 
charcoal  is  used  than  when  coke  is  used  as  fuel.  When  tapped, 
the  slag  is  sometimes  run  into  ladles,  in  which  it  is  carried  to 
the  dump  where  it  is  poured  in  a  molten  condition.  In  other 
cases,  it  is  run  from  the  furnace  into  long  furrows  in  the  ground 


PIG  IRON  49 

from  which  it  is  later  removed  and  taken  to  the  dump.  Some 
of  the  more  modern  plants  run  the  slag  into  pits,  in  some  cases 
20  feet  square  and  20  feet  deep,  and  granulate  it  by  allowing  a 
stream  of  water  to  strike  it  when  leaving  the  trough  at  the 
mouth  of  the  pit.  The  granulated  slag  is  later  removed  from 
the  pit  by  steam  shovels. 

Composition  of  Slag.  —  The  composition  of  a  slag  depends 
upon  the  grade  of  iron  to  be  made  and  the  raw  material  avail- 
able. As  the  composition  of  the  slag  shows  the  condition  of 
the  furnace  and  the  character  of  the  iron  being  produced,  one 
or  more  samples  are  taken  from  each  tap  and  placed  in  iron 
molds.  When  the  furnace  is  in  a  normal  condition,  the  fracture 
of  the  chilled  sample  will  be  gray  in  the  center  and  dark  toward 
the  outside.  If  the  slag  is  basic,  or  " limey,"  the  furnace  is  hot; 
the  fracture  of  a  sample  of  this  slag  will  be  gray  or  white  in  the 
interior.  If  the  slag  is  acid,  or  siliceous,  the  fractured  sample 
will  be  black  or  glassy  and  thin  pieces  will  be  translucent  and, 
in  some  cases,  transparent.  The  iron  produced  with  this  slag 
will  be  very  low  in  silicon  and  high  in  sulphur;  the  slag  will  also 
contain  considerable  iron.  A  cold  furnace  gives  a  dull,  brownish 
slag  that  chills  quickly.  High  manganese  or  manganiferous 
ores  generally  produce  a  green  slag  when  the  furnace  is  working 
well,  and  a  brown  slag  when  it  is  not. 

The  quality  of  an  iron  is  largely  dependent  upon  the  fusibility 
of  its  slag.  A  refractory  slag  produces  a  hot  iron,  because,  as 
it  is  slowly  fused,  it  becomes  superheated  by  long  contact  with 
the  hot  gases.  A  high  hearth  temperature  reduces  the  amount 
of  sulphur  in  the  iron  and  increases  the  amount  of  silicon,  be- 
cause the  hot  slag  has  a  greater  affinity  for  the  sulphur  than  the 
iron,  and  more  silicon  is  reduced  from  its  oxide  and  is  absorbed 
by  the  iron.  The  slag  will  not,  however,  take  up  more  than 
from  2  to  4.5  per  cent  of  calcium  sulphide,  in  any  case. 

The  fusibility  of  a  slag  is  dependent  largely  upon  its  compo- 
sition, the  more  basic  being  the  more  fusible.  Ordinarily,  two- 
thirds  of  the  manganese  in  the  charge  go  into  the  iron,  and  the 
other  third  enters  the  slag;  a  hot  basic  slag  causes  the  manga- 
nese to  go  into  the  iron.  An  acid  slag,  however,  attracts  more 


50  IRON  AND  STEEL 

of  the  manganese  to  itself.  In  the  manufacture  of  ferromanga- 
nese,  dolomite  is  used  as  part  of  the  flux,  as  the  magnesia  tends 
to  reduce  the  loss  of  manganese  in  the  slag. 

Commercial  Uses  of  Slag.  —  Slag  has  been  used  for  many 
purposes  in  an  effort  to  utilize  the  immense  amount  of  waste 
product  that  is  constantly  being  produced.  Among  the  most 
satisfactory  uses  are  its  employment  as  part  of  the  aggregate  in 
concrete,  and  its  manufacture  into  mineral  wool.  The  latter  is 
used  as  a  nonconductor  of  heat,  and  is  packed  between  the  walls 
and  floor  spaces  of  fireproof  buildings,  etc.  One  method  of  mak- 
ing mineral  wool  is  to  melt  the  slag  in  a  cupola  and  then  blow 
the  molten  stream  into  a  long,  narrow  building  by  jets  of  water. 
This  is  effected  by  having  three  flat  streams  of  water  strike  the 
molten  slag  as  it  issues  from  the  slag  hole.  Variations  in  the 
character  of  the  slag  cause  different  grades  of  the  wool,  which  is 
sorted  and  packed  according  to  its  commercial  value.  There 
are  also  differences  in  the  density  of  the  wool  at  every  cast;  the 
lightest  is  blown  the  farthest  from  the  cupola  and  the  heaviest  is 
deposited  nearest  to  it. 

Fuels  for  Blast  Furnaces.  —  The  fuel  used  in  the  blast  furnace 
for  supplying  the  heat  must  be  hard  and  strong  enough  to  sup- 
port the  charge  above  it  without  crushing;  if  crushed  to  a 
powder,  it  will  not  properly  support  the  charge  of  limestone 
and  iron  that  is  placed  above  it.  It  must  be  regular  in  compo- 
sition, free  from  impurities,  and  in  pieces  of  a  good  size  in  order 
that  the  heat  may  pass  through  the  interstices  and  properly 
melt  the  ore.  At  first,  charcoal  was  used  entirely  and  is  still 
preferred  when  an  especially  pure  iron  is  desired.  Anthracite 
and  bituminous  coal  have  also  been  used,  but  coke  is  now  con- 
sidered the  best  for  all  general  purposes,  and  is  the  cheapest. 
Sometimes  anthracite  and  coke  are  mixed,  where  anthracite  is 
easily  obtained,  but  generally  coke  is  used  alone.  For  remelting 
iron,  coke  is  preferred,  aside  from  its  cheapness,  because  it  re- 
quires less  blast  and  melts  the  iron  more  quickly  than  coal, 
although  coal  has  some  advantages  for  this  purpose.  While 
there  is  no  noticeable  difference  in  the  iron  made  with  coke  and 
anthracite,  an  iron  made  with  charcoal  as  a  fuel  is  much  better 


PIG  IRON  51 

than  an  iron  made  with  coke  as  a  fuel.  Not  only  is  the  charcoal 
iron  much  lower  in  sulphur,  but  there  is  some  additional  quality 
that  enables  the  foundryman  to  secure  better  results  with  it  on 
certain  classes  of  work. 

Charcoal.  —  Charcoal  is  the  charred  product  of  wood  and 
was  originally  made  in  mounds,  or  heaps,  from  which  nearly  all 
air  was  excluded.  It  is  very  porous,  light,  and  retains  the  wood 
structure,  but  will  not  withstand  considerable  crushing  pressure. 
It  is  free  from  sulphur,  but  contains  a  small  amount  of  phos- 
phorus, considerable  moisture  and  volatile  matter,  and  from  one- 
half  to  three  per  cent  of  ash.  As  a  rule,  charcoal  is  now  made 
in  retorts,  and  the  waste  gases  pass  to  the  by-product  plant  for 
the  recovery  of  wood  alcohol,  tar,  acetic  acid,  creosote,  etc. 

Anthracite.  —  Anthracite  has  about  the  same  percentage  of 
sulphur,  phosphorus,  and  ash  as  coke.  Its  lack  of  porosity  pre- 
vents the  free  passage  of  the  gases,  and  thus  prevents  the  rapid 
and  regular  burning  of  the  fuel,  and  causes  a  strong  resistance 
to  the  blast.  Besides,  the  coal  tends  to  disintegrate  into  dust 
or  layers  which  are  apt  to  pack  and  clog  the  furnace  and  produce 
serious  furnace  troubles.  At  present,  bituminous  coal  is  used 
to  a  very  limited  extent;  it  can  be  used  only  in  special  moderate- 
sized  furnaces. 

Coke.  —  Coke  is  the  product  obtained  by  expelling  the  vola- 
tile matter  from  certain  bituminous  coals.  It  is  a  strong  smoke- 
less fuel  composed  of  almost  pure  carbon,  and  is  contaminated 
only  by  the  mineral  impurities  that  exist  in  the  coal.  It  should 
be  hard,  strong,  porous,  pure,  and  regular  in  composition.  As 
a  rule,  it  should  have  a  silvery-metallic  luster,  and  the  cells 
should  be  well  connected  and  of  uniform  structure.  It  is  very 
light  and  brittle,  and  depreciates  rapidly  in  shipping.  In  1916, 
the  production  of  the  7500  coke  ovens  in  the  United  States  was 
over  13,000,000  tons  annually. 

As  it  is  carbon  that  furnishes  the  heat,  coke  must  contain 
from  80  to  90  per  cent  of  this  element.  While  some  of  the 
carbon  in  the  coal  is  lost  in  coking,  if  the  process  is  properly 
carried  on,  the  percentage  lost  is  not  large.  The  ash  generally 
ranges  from  9  to  14  per  cent.  The  less  ash  coke  contains,  the 


52  IRON  AND  STEEL 

greater  is  its  value,  as  a  rule,  although  very  low  ash  is  not  desir- 
able in  all  cases,  because  the  ash  is  often  beneficial  in  assisting 
the  formation  of  a  good  slag.  Coke  should  have  the  least  pos- 
sible sulphur  content;  however,  i  per  cent  is  not  always  objec- 
tionable. Sometimes  an  excessive  amount  enters  the  iron, 
although  much  of  it  passes  off  in  the  slag.  The  amount  of  sul- 
phur present  may  be  roughly  told  by  dropping  pieces  of  red-hot 
coke  into  water,  which  drives  off  the  sulphur;  a  comparison  of 
these  pieces  with  the  untested  coke  will  show  approximately 
the  amount  of  sulphur  the  coke  contains.  The  presence  of  over 
0.9  per  cent  of  sulphur  is  often  shown  by  the  odor  of  the  escap- 
ing gases,  while  a  high  sulphur  content  is  often  shown  by  yellow 
spots  or  stains  on  the  surface  of  the  coke.  Quenching  the  coke 
with  impure  water  may  increase  the  sulphur  content. 

The  amount  of  phosphorus  a  coke  may  carry  depends  upon 
various  conditions;  whatever  phosphorus  a  coke  contains  is 
generally  taken  up  by  the  iron  being  made  or  remelted.  When 
the  iron  is  to  be  used  in  the  acid-Bessemer  process,  the  phos- 
phorus in  the  coke  should  not  exceed  from  0.017  to  0.02  per  cent; 
but  for  iron  to  be  used  in  the  open-hearth  process,  the  phos- 
phorus in  the  coke  can  be  much  higher,  because  some  of  the 
phosphorus  in  the  iron  can  be  removed  in  the  steel-making 
process.  Good  fresh  coke  should  not  possess  much  over  i 
per  cent  of  moisture  when  protected  from  rain  and  snow.  The 
less  moisture  the  coke  contains,  the  less  fuel  will  be  required 
when  melting,  on  account  of  the  additional  coke  which  is  needed 
to  evaporate  the  water.  Some  claim  that  exposing  coke  to  the 
weather  reduces  the  sulphur  content,  but  this  fact  has  never 
been  proved. 

At  first,  coke  was  made  like  charcoal  in  large  mounds  or  piles, 
but  this  method  was  wasteful  of  coal  and  did  not  produce  the 
best  results;  besides,  the  time  required  and  the  quality  of  the 
coke  were  affected  by  the  weather.  Most  of  the  coke  in  the 
United  States  is  now  made  in  a  " beehive"  oven.  These  ovens 
are  built  of  firebrick  and  average  12  feet  in  diameter  and  8  feet 
in  height.  They  are  usually  built  in  a  double  row,  the  space 
between  the  ovens  being  filled  with  clay  or  loam.  Pillars  are 


PIG  IRON  53 

placed  between  the  ovens  to  support  the  tracks  upon  which  are 
run  the  cars,  or  larries,  for  charging  the  ovens.  When  the  ovens 
are  to  be  put  "in  blast,"  they  are  brought  to  the  proper  tempera- 
ture by  a  wood  and  coal  fire,  but  the  coking  operation  is  carried 
on  entirely  by  the  heat  retained  by  the  oven  walls  and  that 
given  off  by  the  coal.  This  heat  is  retained  by  the  oven  from 
one  charge  to  another,  so  that  no  additional  heat  need  be  sup- 
plied at  any  time.  The  air  necessary  to  support  combustion  is 
admitted  at,  or  over,  the  surface,  instead  of  passing  through 
the  coal;  this  prevents  the  destruction  of  the  coal  while  burn- 
ing, and  changes  it  to  coke.  The  coking  operation  is  governed 
entirely  by  the  amount  of  air  allowed  to  enter  by  regulating  the 
size  of  this  opening. 

Coking  Process.  —  The  action  of  coking  is  one  of  distillation 
rather  than  combustion.  The  heated  oven  starts  the  distilla- 
tion of  gas,  which  ignites  when  mixed  with  the  air  coming  through 
the  opening  at  the  top  of  the  door.  The  combustion  of  this  gas 
heats  the  dome  of  the  oven,  and  in  about  an  hour  the  coal  is 
ignited.  As  soon  as  this  stage  is  reached,  a  sharp  draft  is  ad- 
mitted to  the  oven.  After  ten  or  twelve  hours,  a  bright  flame 
covers  the  entire  surface  of  the  coal,  which  has  attained  almost 
a  white  heat,  and  passes  through  the  opening  in  the  top.  When 
the  bright  flame  dies  out,  the  coke  is  simply  a  red-hot  mass 
containing  not  much  more  than  i  per  cent  of  the  volatile  matter 
originally  in  the  coal,  the  greater  part  having  passed  off  during 
the  time  in  which  the  coal  was  raised  to  its  highest  temperature. 
When  all  the  gas  is  burnt  off,  the  door  is  removed  and  water  is 
poured  upon  the  glowing  coke  to  quench  it.  In  the  coking 
operation,  the  coal  swells  approximately  one-third  in  volume  for 
Connellsville  coal,  and  varying  amounts  for  others;  after  water- 
ing, the  bulk  is  a  little  less  than  the  whole  charge.  The  coke  is 
then  drawn,  usually  by  men  armed  with  long-handled  scrapers, 
who  let  the  coal  fall  upon  the  platform  at  the  door  of  the  oven. 
It  is  later  loaded  into  cars  for  shipment.  The  care  exercised  and 
the  time  taken  in  drawing  the  coke  from  the  oven  has  much  to 
do  with  its  size,  freedom  from  "  braise,"  or  small  coke,  and  the 
yield.  In  large  plants,  and  especially  when  labor  is  scarce,  the 


54  IRON  AND   STEEL 

coke  is  drawn  by  mechanical  devices  which  load  it  directly  into 
the  cars;  this  method,  however,  breaks  the  coke  much  more 
than  the  hand  drawing.  At  one  time,  the  coke  was  drawn  and 
then  quenched,  but  the  present  method  is  not  only  less  laborious, 
but  the  coke  is  practically  free  from  moisture,  and  retains  the 
characteristic  silver-gray  luster. 

Varieties  of  Beehive  Oven  Coke.  —  Beehive  ovens  are  gen- 
erally operated  to  produce  48-  and  72-hour  coke,  but  96-hour 
coke  is  made  in  special  cases.  There  is  practically  no  difference 
in  the  cokes,  as  a  little  more  coal  is  charged  for  the  longer  periods 
to  continue  the  coking  process.  The  usual  practice  is  to  charge 
about  five  tons  of  coal,  in  the  ordinary  1 2-foot  oven,  during  the 
first  four  days  of  the  week,  and  six  tons  on  Friday  and  Saturday ; 
this  plan  makes  it  unnecessary  to  draw  the  ovens  on  Sunday. 
"  Black  butts"  are  the  uncoked  ends  of  coal  that  lay  on  the 
bottom  of  the  oven.  "  Black  tops"  are  caused  by  the  crown  of 
an  oven  becoming  so  hot  as  to  fuse  the  top  surface  of  the  coal 
and  thus  prevent  the  free  escape  of  the  gases;  these  will,  there- 
fore, deposit  lampblack  in  the  cells  of  the  coke  that  is  being 
formed.  " Stock  coke"  is  the  name  given  coke  that  has  been 
stored  in  piles  at  the  coke  works.  Because  of  the  additional 
handling  it  receives,  this  coke  is  in  much  smaller  lumps  than  the 
other.  It  also  contains  more  moisture  and  dirt,  as  it  is  exposed 
to  rain,  snow,  dust,  and  smoke. 

Advantages  of  the  Beehive  Ovens.  —  The  beehive  oven  has 
the  advantage  of  low  initial  cost,  simplicity  of  operation,  and 
the  production  of  the  best  possible  coke.  It  also  has  a  low  cost 
of  maintenance,  because  it  can  be  operated  by  unskilled  labor, 
besides,  operations  can  be  discontinued  and  resumed  with  less 
inconvenience  and  expense  than  with  the  retort  oven.  In  order 
to  lessen  the  waste,  some  plants  now  use  the  gases  from  the 
ovens  for  the  generation  of  steam  in  boilers,  thus  using  both  the 
combustible  part  and  the  heat  the  gases  contain.  In  such  a 
case,  all  the  ovens  are  connected  by  a  large  flue  for  the  passage 
of  the  gases. 

Coking  Coals.  —  For  coking,  coal  should  be  as  free  as  pos- 
sible of  sulphur,  phosphorus,  and  ash.  Some  of  the  sulphur  is 


PIG  IRON  55 

driven  off  in  the  coking  operation,  but  the  phosphorus  and  ash 
remain  unchanged.  As  a  result,  the  coke  has  a  higher  percentage 
of  these  properties  than  the  coal,,  because  it  requires  practically 
ij  ton  of  coal  to  make  one  ton  of  coke.  In  order  to  increase  the 
coals  available  for  coking,  coal  that  contains  considerable  slate 
or  iron  pyrites  is  used  after  it  has  been  cleaned.  This  cleaning 
may  be  done  by  the  wet  or  the  dry  method,  the  former  being 
preferred.  In  either  case,  the  aim  is  to  remove  the  greatest 
amount  of  impurities  with  the  least  amount  of  coal  passing  off 
with  the  dirt. 

The  "dry"  method  is  the  cheaper,  as  it  consists  only  of  the 
crushing  and  screening  of  the  coal.  This  crushing  is  so  effected 
that  the  coal  is  broken  small  enough  to  pass  through  screens, 
while  the  impurities,  which  are  harder,  are  too  large.  In  the 
"wet"  method,  the  coal  is  separated  from  the  heavier  impuri- 
ties by  "jigs."  The  coal,  which  is  first  crushed,  is  carried  by 
water  to  tubs  in  which  it  is  constantly  agitated,  so  that  the 
heavier  substances  settle  at  the  bottom,  while  the  coal  floats 
off.  The  washing  process,  however,  often  removes  so  much 
bituminous  coal  with  the  slate  as  to  rob  the  coal  of  most  of  its 
coking  qualities.  Coke  made  from  washed  coal  contains  less 
ash  and  sulphur  than  that  made  from  unwashed  coal. 

By-product  Coke  Ovens.  —  Retort  ovens  were  first  used  for 
coking  coals  that  could  not  be  satisfactorily  coked  in  the  bee- 
hive oven.  In  its  simplest  form,  the  retort  oven  is  a  firebrick 
chamber  surrounded  by  heating  flues  and  provided  with  a  pipe 
through  which  the  products  of  distillation  may  be  carried  off. 
After  the  chamber  is  filled  with  coal  and  sealed,  the  heat  in  the 
surrounding  flues  breaks  up  the  coal  and  drives  off  the  volatile 
matter,  leaving  the  coke  behind.  This  volatile  matter  passes 
through  apparatus  which  separates  the  tar  and  ammonia  from 
the  gas.  About  one-half  the  gas  is  used  for  heating  the  oven, 
and  the  rest  is  valuable  for  power,  illumination,  or  for  other 
purposes.  In  many  cases,  these  ovens  complete  the  coking  proc- 
ess in  twenty-four  hours.  In  the  best  American  practice,  this 
time  has  been  reduced  to  eighteen  hours.  Good  coke  has  been 
made  in  less  time  than  this,  but  the  high  temperature  neces- 


56  IRON  AND  STEEL 

sary  causes  a  rapid  deterioration  of  the  oven;  besides,  as  the 
time  is  reduced,  the  amount  of  tar  and  ammonia  obtained  is 
lessened. 

Among  the  principal  types  of  ovens  in  the  United  States  are 
the  Semet-Solvay,  Koppers,  Otto,  and  Coppee.  The  ovens  in 
most  common  use  are  modifications  of  the  Coppee  vertical-flue 
oven  and  the  Simon-Carves  horizontal-flue  oven.  In  any  case, 
however,  an  installation  consists  of  a  number  of  simple  ovens 
built  side  by  side  to  form  a  battery.  In  general,  the  ovens  are 
from  35  to  40  feet  long,  10  feet  high,  and  from  17  to  22  inches 
wide,  the  average  width  being  19  inches.  While  ovens  having 
a  capacity  of  13  J  tons  are  in  successful  operation,  some  engineers 
advise  limiting  the  size  to  \i\  tons.  The  oven,  or  retort,  usu- 
ally tapers  about  4  inches,  being  widest  at  the  discharge  end. 
This  provides  room  for  the  coal  to  swell  and  there  will  be  less 
resistance  offered  to  the  moving  of  the  coke.  The  ends  of  many 
ovens  are  closed  by  iron  doors  lined  with  firebrick,  which  fit 
closely  and  are  luted  with  clay.  In  the  latest  ovens,  the  doors 
are  plug-shaped  and  go  into  the  oven  far  enough  to  hold  the 
coal  at  the  level  of  the  first  flue.  This  arrangement  prevents 
the  formation  of  black  ends,  because  of  coal  projecting  beyond 
the  flues.  Like  the  beehive  oven,  the  tops  of  the  chambers  have 
openings  through  which  the  coal  is  charged.  The  ovens  are 
level  and  the  coke  is  pushed  out  by  means  of  mechanical  de- 
vices. Sometimes  the  coke  is  watered  inside  the  closed  recep- 
tacle which  causes  the  coke  to  retain  its  silvery  appearance,  but 
more  often  the  quenching  takes  place  as  the  coke  is  pushed 
from  the  oven  into  a  car  stationed  at  the  discharge  end  of  the 
oven. 

Horizontal-flue  Type.  —  In  most  horizontal-flue  ovens,  each 
oven  in  a  battery  is  a  separate  unit  so  that  its  working  is  en- 
tirely independent  of  the  others.  The  latest  form  of  Semet- 
Solvay  oven  has  six  horizontal  flues  in  each  side  of  the  coal 
chamber,  while  an  1 8-inch  wall  separates  the  ovens  in  the  bat- 
tery. After  the  oven  is  charged,  the  gas  for  the  combustion  is 
admitted  to  the  flue  by  a  burner  at  the  end.  The  combustion 
starts  in  the  top  flue,  as  the  gas  and  fresh  air  admitted  through 


PIG  IRON  57 

each  flue  is  just  enough  to  maintain  a  uniform  temperature. 
In  order  to  allow  for  the  greater  volume  of  the  products  of  com- 
bustion, the  flues  gradually  increase  in  size  until  the  bottom 
flue  is  reached;  this  is  reduced  in  size  as  only  a  part  of  the  prod- 
ucts of  combustion  pass  through  it. 

The  gases  from  the  coal  chamber  are  carried  to  a  condensing 
house  where  the  by-products  are  removed.  Part  of  the  gas  is 
then  returned  to  heat  the  oven,  while  part  may  be  used  for 
lighting  or  power  purposes.  In  a  non-regenerative  oven,  the 
gases  are  wasted  as  soon  as  they  pass  through  the  oven  flues. 
In  regenerator  ovens,  the  gases  pass  through  the  regenerator 
at  the  other  end  of  the  oven  through  which  they  were  ad- 
mitted, and  heat  its  checker-work.  Each  oven  in  the  latest 
type  has  a  regenerator  at  each  end,  through  which  the  air  passes 
on  its  way  to  the  flues.  All  the  regenerators  in  a  battery,  which 
usually  contains  about  50  or  60  ovens,  are  operated  at  one 
time. 

Vertical-flue  Type.  —  In  most  vertical-flue  ovens,  adjoining 
coal  chambers  have  one  gas  chamber  between  them.  In  the 
Koppers  oven,  the  charge  is  subjected  to  a  uniform  heat,  because 
there  are  thirty  vertical  flues  in  each  side  of  the  oven,  which  is, 
therefore,  heated  by  the  combustion  of  gas  at  sixty  different 
points. 

Recovery  of  By-products.  —  Ordinary  Connellsville  coal  con- 
tains approximately  62.5  per  cent  of  fixed  carbon  and  28.36  per 
cent  of  volatile  matter.  In  other  words,  over  one-quarter  of 
the  coal  evaporates  and  passes  off  in  the  coking  process.  This 
volatile  matter  gives  a  gas  that  is  rich  in  methane,  or  marsh  gas, 
and  hydrogen.  The  average  composition  of  gas  from  the  Semet- 
Solvay  type  of  oven  is  as  follows:  Hydrogen,  from  40  to  50  per 
cent;  methane,  35  per  cent;  nitrogen,  from  4  to  8  per  cent; 
benzines,  from  2  to  3  per  cent;  carbon  dioxide,  i  per  cent;  car- 
bon monoxide,  i  per  cent;  oxygen,  0.5  per  cent.  The  calorific 
value  of  this  gas  averages  500  B.T.U.  per  cubic  foot.  Ovens, 
however,  have  been  constructed  that  are  so  free  from  leaks  that, 
for  each  ton  of  coal  coked,  they  give  off  over  6000  cubic  feet  of 
gas  having  a  value  of  590  B.T.U.  Besides,  there  is  obtained  tar 


58  IRON  AND   STEEL 

suitable  for  pavements  and  roofs,  benzol,  and  ammonia.  In 
addition,  the  yield  of  coke  is  greatly  increased,  one  ton  of  coal 
giving  70  per  cent  of  its  weight  in  coke,  in  comparison  with  60 
per  cent  obtained  in  the  beehive  oven. 

The  amount  of  by-products  recovered,  however,  varies  with 
the  nature  of  the  coal  used  and  the  coking  period.  Under 
average  conditions,  a  ton  of  coal  in  addition  to  its  coke  will  yield 
6000  cubic  feet  of  gas;  7  gallons  of  tar;  from  20  to  25  pounds  of 
ammonium  sulphate;  and,  if  suitable  apparatus  is  available,  from 
i.i  to  3.8  gallons  of  benzol,  and  0.3  gallon  of  toluol.  If  the 
surplus  gas  is  used  for  fuel  purposes  alone,  only  one  gas  main  is 
necessary  along  the  top  of  the  oven.  If  the  gas  is  used  for 
illuminating,  or  for  other  purposes,  two  mains  must  be  installed. 
One  main  is  then  used  for  the  rich  gas  evolved  during  the  first 
period  of  coking,  and  the  other  for  the  poorer  or  fuel  gas.  This 
separation  is  also  made  in  many  plants  in  connection  with  iron 
and  steel  works  which  desire  a  rich  gas  for  their  gas  engines 
and  a  lean  gas  for  the  heating  of  furnaces,  etc. 

In  the  by-product  plant,  after  the  gas  has  cooled,  the  tar  is 
extracted,  naphthalene  is  " thrown  down"  as  far  as  possible, 
and  the  ammonia  is  scrubbed  out  of  the  gas  and  passed  through 
dilute  sulphuric  acid,  so  as  to  form  sulphate  of  ammonia.  In 
some  plants,  however,  the  gas  is  passed  through  a  saturator 
after  the  tar  has  been  separated,  thus  rendering  the  scrubbing 
of  the  ammonia  unnecessary.  The  value  of  by-products  re- 
covered from  American  coke  manufacture  in  1915  was  nearly 
$30,000,000.  Although  there  were  material  increases  in  the 
output  and  value  of  gas,  tar,  and  ammonia,  the  value  of  the 
benzol  products  rose  from  less  than  $1,000,000  in  1914^0  more 
than  $7,760,000  in  1915. 

Flux  used  in  Blast  Furnace.  —  A  flux  is  used  in  the  smelting 
of  iron  ore  in  a  blast  furnace  in  order  to  make  the  non-metallic 
residue  of  the  ore  and  ash  of  the  fuel  more  fluid,  so  that  they 
will  flow  out  of  the  furnace  in  the  form  of  slag.  This  slag  must 
have  such  a  composition  that  it  will  melt  when  it  reaches  the 
melting  zone  of  the  blast  furnace,  fluid  enough  to  run  out  through 
the  cinder  notch,  and  rich  enough  in  lime  to  supply  the  lime 


PIG  IRON  59 

needed  for  the  desulphurizing  reaction.  The  flux  almost  uni- 
versally used  is  limestone,  which  is  available  in  nearly  all 
iron-making  localities.  Magnesia  is  also  sometimes  used.  Dolo- 
mite, often  called  " magnesia  limestone,"  has  also  been  success- 
fully used,  but  furnace  men  generally  prefer  limestone,  as  they 
claim  that  dolomite  is  not  as  active  a  desulphurizing  agent  as 
limestone.  Some  iron  ores  contain  sufficient  limestone  or  mag- 
nesia to  form  a  fusible  slag,  but  generally  some  additional  flux 
is  provided.  The  limestone  or  other  fluxes  are  used  in  the 
condition  in  which  they  are  mined.  Limestone,  if  roasted,  will 
more  readily  unite  with  impurities,  but  the  cost  of  the  treatment 
offsets  any  saving  that  may  thus  be  effected.  The  amount 
of  flux  required  depends  primarily  upon  the  silica  in  the  flux 
and  in  the  rest  of  the  charge;  for  ordinary  pig  iron,  using  Lake 
Superior  ores,  about  1000  pounds  per  ton  of  iron  may  be  taken 
as  an  average. 

Effect  of  Various  Elements  on  Pig  Iron.  —  The  manganese, 
phosphorus,  silicon,  and  sulphur  present  in  pig  iron  all  have  a 
different  influence  upon  the  characteristics  of  the  iron.  Sulphur 
and  silicon  tend  to  segregate  in  the  iron  and  are,  therefore, 
generally  found  unevenly  distributed  through  it.  The  content 
of  sulphur  is  likely  to  be  found  highest  near  the  top  of  the  pig. 
The  presence  of  soft  gray  spots  is  an  indication  of  the  segregation 
of  silicon.  The  remelting  of  the  pig  iron  usually  makes  it  more 
'uniform  in  composition;  hence,  the  remelting  of  the  pig  iron  in 
the  cupola  furnace  for  making  iron  castings  improves  the  metal 
in  the  pig. 

Influence  of  Manganese.  —  In  pig  iron  the  content  of  man- 
ganese ranges  from  a  trace  to  about  3  per  cent.     For  pig  iron 
intended  for  making  castings,  more  than  i  per  cent  of  manganese 
for  light  castings,  or  2  per  cent  for  heavy  castings  requiring  \ 
strength,  may  prove  injurious;    but  when  used  in  moderate  j' 
percentages  it  strengthens  the  iron,  deepens  the  chill,  and,  in 
cupola  work,  assists  in  eliminating  the  sulphur.     By  this  elimi-l 
nation  of  the  sulphur,  softer  castings  are  obtained.     Manganese    v 
increases  the  time  required  for  the  molten  metal  to  solidify.     The 
condition  of  the  blast  furnace  determines  to  a  large  extent  the 


60  IRON  AND   STEEL 

percentage  of  manganese  in  the  pig  iron,  as  a  cold-working  fur- 
nace will  tend  to  pass  off  the  manganese  into  the  slag,  while  a 
hot-working  furnace  will  pass  it  into  the  pig  iron. 

Influence  of  Phosphorus.  —  Phosphorus  has  a  very  decided 
influence  on  the  castings  made  from  pig  iron.  Over  0.75  per 
cent  is  likely  to  cause  the  iron  to  be  cold-short  and  over  1.3 
per  cent  will  appreciably  harden  the  iron.  Phosphorus  is 
present  in  pig  iron  in  amounts  ranging  from  a  trace  to  1.5  per 
cent.  Pig  iron  having  less  than  o.i  per  cent  of  phosphorus  can 
be  used  for  the  Bessemer  process.  That  having  more  than  o.i 
per  cent  of  phosphorus  can  only  be  used  for  the  open-hearth 
process  and  for  foundry  iron.  Phosphorus  adds  to  the  fluidity 
of  the  molten  metal,  but,  when  present  in  large  percentages, 
weakens  the  metal  more  than  any  other  element. 

Influence  of  Silicon.  —  The  permissible  silicon  content  in  pig 
iron  depends  upon  the  sulphur  and  manganese  content.  If 
the  content  of  sulphur  and  manganese  is  low,  that  of  silicon 
should  be  low,  and  unless  the  sulphur  and  manganese  content  is 
high,  the  pig  iron  should  not  contain  more  than  3  per  cent  of 
silicon.  Additional  silicon  will  produce  castings  that  are  brittle 
or  " rotten  short." 

Influence  of  Sulphur.  —  Pig  iron  usually  contains  from  0.03 
to  o.io  per  cent  of  sulphur.  Sulphur  causes  iron  to  be  "red- 
short"  as  well  as  "  cold-short, "  that  is,  the  iron  is  brittle  either 
when  heated  to  a  red  heat  or  when  cold.  The  sulphur  in  pig 
iron  is  mainly  derived  from  the  fuel  in  the  blast  furnace.  On 
the  one  hand  it  increases  the  strength  of  the  iron  and  makes  it 
harder,  but,  on  the  other,  it  is  likely  to  make  light  castings  too 
hard  and  cause  blow-holes.  The  amount  of  sulphur  that  pig 
iron  absorbs  from  the  fuel  depends  upon  the  condition  of  the 
furnace.  A  greater  amount  of  sulphur  is  absorbed  in  a  furnace 
that  is  working  cold.  A  properly  or  hot-working  furnace  sends 
the  sulphur  into  the  slag.  Generally  speaking,  in  iron  made  with 
coke,  the  lower  the  silicon,  the  higher  the  percentage  of  sulphur. 
Charcoal  is  low  in  sulphur,  and,  hence,  charcoal  pig  iron  contains 
less  sulphur  than  anthracite  or  coke  pig  iron,  and  is,  therefore, 
superior  for  many  kinds  of  castings. 


PIG  IRON  6 1 

Classification  and  Grading  of  Pig  Iron.  —  Pig  iron  is  classified 
and  graded  in  so  many  different  ways  that  it  is  impossible  to 
give  any  uniform  or  consistent  method  of  classification.  In  a 
general  way,  however,  it  may  be  said  that  there  are  three  methods 
of  classifying  pig  iron;  (i)  according  to  its  composition;  (2) 
according  to  its  intended  use;  and  (3)  according  to  the  method 
by  means  of  which  it  has  been  manufactured. 

Grading  According  to  Composition  or  Fracture.  —  With  regard 
to  composition,  which  is  the  modern  method  of  classifying 
pig  iron,  such  terms  as  "high-silicon  pig,"  " low-phosphorus 
pig,"  etc.,  are  used  to  indicate  some  important  consideration  in 
the  composition.  In  modern  practice,  the  classification  accord- 
ing to  composition  is  made  by  chemical  analysis,  but  up  to  com- 
paratively recent  years,  the  practice  was  to  merely  examine  the 
fracture  of  a  broken  pig.  When  the  silicon  content  is  low  and 
the  combined  carbon  high,  the  fracture  is  white,  but,  when  the 
silicon  is  high,  the  fracture  is  more  silver-gray,  and  if  the  carbon 
is  mainly  in  the  form  of  graphite,  the  fracture  is  a  dull  gray. 
When  graded  in  accordance  with  the  fracture,  the  ordinary 
grades  of  pig  iron  are  No.  i,  No.  2,  No.  3,  "mill,"  and  " white." 
Sometimes,  when  close  grading  is  desired,  intermediate  grades 
are  used;  thus,  No.  2X  will  be  between  No.  2  and  No.  i  irons. 
No.  i  iron  has  a  dark  gray  fracture  and  its  grain  has  large  and 
uniform  crystals  of  graphite  to  the  extreme  edge.  No.  2  is 
lighter  in  color  and  has  a  grain  with  smaller  crystals.  No.  3 
iron  is  still  lighter  in  color  and  is  close-grained.  Mill  iron  has 
a  uniform  dull  gray  color,  and  has  no  suggestion  of  grain;  its 
color  depends  largely  upon  the  amount  of  silicon  present.  White 
iron  is  chilled  throughout  the  section,  as  nearly  all  the  carbon 
is  combined;  it  is  high  in  sulphur  and  low  in  silicon. 

Classification  According  to  Use.  —  With  regard  to  the  use  for 
which  the  pig  iron  is  intended,  there  are  a  great  many  different 
names,  such  as  foundry  iron,  malleable  pig  iron,  chilling  iron, 
Bessemer  pig  iron,  basic  pig  iron,  gray  forge  iron,  ferrosilicon 
pig  iron,  mottled  pig  iron,  and  white  pig  iron. 

Foundry  Pig  Iron.  —  Foundry  pig  iron  is  made  either  with 
coke  or  anthracite  fuel,  and  is  used  for  the  making  of  both  chilled 


62  IRON  AND   STEEL 

and  unchilled  castings.  It  generally  contains  from  i  to  4  per 
cent  of  silicon;  from  o.oi  to  0.05  per  cent  of  sulphur;  from  0.2 
to  1.5  per  cent  of  phosphorus;  and  from  a  mere  trace  to  1.5 
per  cent  of  manganese.  Softeners  are  foundry  pig  irons  which 
are  high  in  silicon  and  usually  high  in  phosphorus,  and  which 
are  mixed  with  lower  silicon  irons  or  with  mixtures  that  carry 
a  considerable  amount  of  scrap,  in  order  to  produce  a  soft  casting. 
These  pig  irons  contain  from  2.5  to  5  per  cent  of  silicon  with 
from  0.2  to  0.3  per  cent  of  phosphorus.  Malleable  pig  iron, 
which  is  used  for  making  malleable  cast-iron  castings,  must  con- 
tain less  than  0.05  per  cent  of  sulphur,  while  the  phosphorus 
content  may  vary  from  0.05  to  0.2  per  cent;  the  manganese  con- 
tent, from  0.5  to  0.75  per  cent;  and  the  silicon  content,  from  0.6 
to  1.25  per  cent.  Chilling  iron  is  used  for  iron  castings  that  re- 
quire a  hard  surface.  It  is,  therefore,  low  in  silicon  and  high  in 
sulphur.  The  latter  element  increases  the  chilling  tendency,  but 
the  pig  iron  must  not  contain  so  much  sulphur  as  to  affect  the 
strength  of  the  casting  when  the  strength  is  essential.  As  a  rule, 
the  silicon  content  generally  ranges  from  o.i  to  0.4  per  cent 
with  from  0.5  to  i  per  cent  of  manganese.  The  phosphorus 
content  must  be  less  than  0.3  per  cent. 

Bessemer  Pig  Iron.  —  Bessemer  pig  iron  is  made  with  either 
coke  or  anthracite  as  a  fuel,  and  is  used  chiefly  for  the  making 
of  acid  Bessemer  and  acid  open-hearth  steel,  although  it  may 
also  be  used  as  a  foundry  iron  for  heavy  castings  which  do  not 
require  a  very  fluid  metal.  Bessemer  pig  iron  contains  from 
0.75  to  2.5  per  cent  of  silicon;  from  o.oi  to  0.05  per  cent  of  sul- 
phur; and  from  0.2  to  i  per  cent  of  manganese.  It  must  not 
contain  more  than  o.i  per  cent  of  phosphorus.  If  it  contains  a 
greater  percentage  than  this,  it  is  called  "  off  -Bessemer."  Pig 
iron  is  often  classified  as  Bessemer  and  non-Bessemer  iron,  ac- 
cording to  whether  the  phosphorus  content  is  less  or  more  than 
o.i  per  cent. 

Basic  Pig  Iron.  —  Basic  pig  iron  is  used  chiefly  in  the  basic 
open-hearth  furnace  for  making  steel.  This  pig  iron  is  cast 
in  chilled  molds  or  magnesia  sand.  It  is  similar  in  character 
to  gray  forge  iron  (see  following  paragraph)  but  its  sulphur 


PIG  IRON  63 

content  must  not  exceed  0.05  per  cent.  In  pig  iron  for  the  open- 
hearth  process,  the  phosphorus  should  also  be  kept  low,  but  need 
not  be  as  low  as  in  Bessemer  pig  iron.  It  may  range  from  0.2 
to  2.5  per  cent.  The  silicon  content  should  be  less  than  i  per 
cent,  and  the  manganese  content  may  range  from  0.3  to  i  per 
cent. 

Gray  Forge  Iron.  —  Gray  forge  pig  iron  is  used  chiefly  in  the 
puddling  furnace  for  making  wrought  iron  and  in  the  foundry 
for  casting  water  pipes  and  similar  castings,  in  which  case  it  is 
sometimes  mixed  with  pig  iron  having  a  higher  silicon  content. 
Gray  forge  iron  has  a  gray  fracture  with  little  or  no  grain.  Its 
sulphur  content  varies  from  0.03  to  0.2  per  cent,  and  its  silicon 
content,  from  0.5  to  2  per  cent. 

Ferrosilicon  Pig  Iron.  —  Ferrosilicon  pig  iron,  also  known  as 
" silvery  pig  iron,"  is  made  from  ores  containing  silicon,  and  an 
excessive  amount  of  fuel  is  used  to  produce  high  temperatures  in 
the  furnace.  Ferrosilicon  pig  iron  may  be  made  either  with 
coke  or  with  a  mixture  of  coke  and  coal  as  a  fuel.  It  is  used  in 
the  Bessemer  and  open-hearth  processes  to  increase  the  silicon 
content.  It  contains  from  6  to  16  per  cent  of  silicon.  It  has  a 
large,  open  grain  and  is  often  used  as  a  " softener." 

Mottled  and  White  Pig  Iron.  —  Mottled  and  white  pig  irons 
are  used  for  hard  chilled  castings.  They  are  made  with  either 
coke,  anthracite  coal,  or  charcoal  as  a  fuel,  and  usually  contain 
a  high  percentage  of  carbon.  The  percentage  of  silicon  may 
range  from  o.i  to  i  per  cent;  of  sulphur,  from  0.05  to  0.3  per 
cent;  of  manganese,  from  o.i  to  1.5  per  cent;  and  of  phosphorus, 
from  0.3  to  0.5  per  cent. 

Spiegeleisen.  —  Spiegeleisen  may  be  considered  as  a  pig  iron 
which  is  very  rich  in  manganese.  It  is  used  for  increasing  the 
manganese  content  in  steel,  in  the  Bessemer  and  open-hearth 
processes.  It  contains  from  10  to  25  per  cent  of  manganese. 
The  alloy  known  as  "  f erromanganese "  contains  from  70  to 
80  per  cent  of  manganese,  from  6  to  7  per  cent  of  carbon,  with 
the  remainder  iron. 

Scotch  Pig  Iron.  —  Scotch  pig  iron,  which  may  contain  from 
3  to  5  per  cent  of  silicon,  is  used  as  a  softener,  particularly  when 


64  IRON  AND   STEEL 

castings  with  a  high  silicon  content  are  required.     This  pig 
iron  has  a  large  open  grain  and  is  dark  in  color. 

Classification  according  to  Method  of  Manufacture.  —  With 
regard  to  the  methods  of  manufacture,  pig  iron  may  be  classified 
as  coke  pig,  anthracite  pig,  and  charcoal  pig.  As  the  name  in- 
dicates, coke  pig  iron  is  smelted  with  coke;  anthracite  pig  iron 
is  smelted  with  anthracite  coal  mixed  with  coke;  and  charcoal 
pig  iron  is  smelted  with  charcoal.  This  latter  kind  is  superior  to 
other  brands  of  pig  iron  when  melted  in  an  air  furnace.  It  is 
generally  used  for  the  manufacture  of  castings  for  guns,  hydraulic 
and  steam  cylinders,  and  for  chilled  castings.  It  can  be  made 
freer  from  silicon,  phosphorus,  and  sulphur  than  coke  or  an- 
thracite irons.  It  generally  contains  from  0.5  to  2  per  cent  of 
silicon;  from  a  trace  to  1.5  per  cent  of  manganese;  and  from  0.15 
to  0.75  per  cent  of  phosphorus.  The  sulphur  content  must  not 
exceed  0.08  per  cent.  The  silicon  may  sometimes  be  as  high 
as  5  per  cent.  Charcoal  pig  iron  is  usually  graded  in  a  series  of 
numbers  which  vary  according  to  the  silicon  content,  each 
number  indicating  an  increase  of  0.2  per  cent  of  silicon. 


CHAPTER  IV 
WROUGHT  IRON  AND  ITS  MANUFACTURE 

IRON  articles  were,  at  one  time,  made  by  smelting  the  ore  in 
an  open  hearth  and  hammering  the  pasty  mass  until  most  of 
the  cinders  and  impurities  were  worked  out.  The  metal  was 
then  beaten  into  the  desired  shape.  The  metal  obtained  in 
this  way  was  wrought  iron,  and  the  quality  of  the  metal  in  the 
articles  produced  by  this  method  was  excellent.  The  develop- 
ment of  blast  and  cupola  furnaces,  however,  made  available  the 
use  of  large  quantities  of  molten  iron,  so  that  the  more  easily 
manufactured  iron  castings  soon  displaced  the  hammered  metal 
for  many  purposes.  Later,  the  development  of  the  steel  industry 
still  more  restricted  the  use  of  wrought  iron.  Nevertheless,  a 
large  field  remains  where  its  resistance  to  continued  stress  and 
the  ease  with  which  it  can  be  welded  renders  it  valuable.  Where 
reliability  is  of  prime  importance,  no  material  anywhere  near 
within  its  price  is  superior  to  it.  At  present,  wrought  iron  is 
used  for  spikes,  nails,  bars,  nuts,  wire,  chain,  crane  hooks, 
horseshoes,  sheets,  plates,  staybolts,  piping,  third  rails,  armatures, 
electromagnets,  and  in  the  manufacture  of  crucible  steel.  Years 
ago,  marine  engine  shafting  was  invariably  made  from  wrought 
iron.  The  firm  of  Blair  of  Stockton-on-Tees,  one  of  the  earliest 
makers  of  marine  engines  and  one  of  the  most  conservative 
firms. at  the  present  time,  still  makes  (or,  at  least,  until  very 
recently  made)  its  shafting  from  this  material.  Two  leading 
British  makers  of  steam  fire  engines  still  use  wr ought-iron  plates 
for  their  boilers.  These  boilers  are  capable  of  being  subjected 
to  very  heavy  duty  in  spite  of  their  small  size.  In  British  loco- 
motive practice,  wrought-iron  rivets  are  still  used  for  the  boilers. 

Characteristics  of  Wrought  Iron.  — Wrought  iron,  chemically 
considered,  is  the  purest  form  of  commercial  iron,  as  it  contains  a 
comparatively  small  amount  of  carbon,  averaging  about  o.i, 

65 


66  IRON  AND   STEEL 

ranging  from  as  little  as  0.05  to  0.3  per  cent.  It  contains,  how- 
ever, a  considerable  amount  of  slag  mechanically  mixed  with  it. 
Wrought  iron  is  very  malleable,  and  at  a  bright  red  heat  it  may 
be  hammered  or  rolled  into  almost  any  desired  shape,  while  at 
a  white  heat  it  can  easily  be  welded.  It  is  one  of  the  most  duc- 
tile of  the  metals,  but  unlike  steel  it  does  not  harden  to  any  ap- 
preciable extent  when  heated  to  a  full  red  heat  and  suddenly 
cooled  by  quenching.  It  requires  a  higher  temperature  for 
melting  than  any  of  the  other  commercial  forms  of  iron  and 
steel,  and  the  molten  metal  cannot  be  cast  in  a  mold.  When 
wrought  iron  is  broken  by  tension  or  bending,  a  good  quality 
of  the  metal  shows  a  fibrous  structure;  but,  if  it  is  subjected  to 
shock  or  continuous  alternating  stresses  exceeding  the  elastic 
limit,  the  molecular  structure  becomes  crystalline.  Good 
wrought  iron  will  not  break  suddenly  unless  the  molecular 
structure  has  thus  been  transformed,  but  will  give  warning  of 
excessive  stresses  by  the  gradual  extension  of  the  metal  before 
breaking.  Material  that  has  become  crystalline  may  be  brought 
back  to  the  fibrous  condition  by  heat-treatment,  generally  known 
as  "annealing";  crane  chains,  for  instance,  are  thus  frequently 
annealed  in  order  to  retain  their  original  tenacity. 

Wrought  iron  has  a  specific  gravity  of  from  7.6  to  7.85.  It 
melts  at  approximately  2700  degrees  F.,  and  has  a  linear  expansion 
per  unit  length  per  degree  F.  of  0.0000065.  Its  electric  conduc- 
tivity is  about  one-sixth  that  of  silver. 

Strength  of  Wrought  Iron.  — As  wrought  iron  is  made  in 
several  different  grades  and  qualities,  definite  figures  as  to  its 
strength  cannot  be  given,  but  it  may  be  said  in  general  terms 
that  wrought  iron  has  a  tensile  strength  varying  from  40,000 
to  50,000  pounds  per  square  inch;  a  compressive  strength  of 
from  40,000  to  45,000  pounds  per  square  inch;  and  a  modulus 
of  elasticity  of  27,000,000.  The  best  grade  of  wrought  iron  has 
about  the  following  physical  characteristics:  Ultimate  strength 
in  tension,  50,000  pounds  per  square  inch;  ultimate  strength  in 
compression,  50,000  pounds  per  square  inch;  elastic  limit  in 
tension,  30,000  pounds  per  square  inch;  elastic  limit  in  torsion, 
20,000  pounds  per  square  inch;  elastic  limit  in  compression, 


WROUGHT  IRON  67 

from  20,000  to  25,000  pounds  per  square  inch;  modulus  of  elas- 
ticity in  tension,  28,000,000;  modulus  of  elasticity  in  torsion, 
12,800,000;  elongation  in  eight  inches,  20  per  cent;  and  reduc- 
tion of  area,  30  per  cent. 

The  strength  of  wrought  iron  is  affected  by  its  chemical  com- 
position, and  the  mechanical  working  and  heat-treatment  to 
which  it  has  been  subjected.  Wrought  iron  has  a  well-defined 
yield-point  in  both  tension  and  compression,  which  is  from  2000 
to  4000  pounds  per  square  inch  lower  than  the  proportionate 
elastic  limit.  Beyond  the  yield-point,  wrought  iron  acts  as  a 
plastic  material  which  flows  rapidly  as  the  ultimate  strength  is 
approached.  The  ultimate  strength  in  tension  increases  with 
the  amount  of  carbon.  It  is  estimated  that  iron  very  free 
from  carbon  has  a  strength  of  about  40,000  pounds  per  square 
inch.  The  strength  of  wrought  iron  increases  with  an  increase  of 
temperature  up  to  about  500  or  600  degrees  F.,  after  which  the 
strength  rapidly  decreases.  The  percentage  of  elongation  de- 
creases as  the  temperature  is  raised  up  to  300  degrees  F.,  but 
increases  above  this  point. 

Classification  of  Wrought  Iron.  —  Wrought  iron  is  classified 
and  graded  in  so  many  different  ways  that  it  is  impossible  to 
name  any  system  that  could  be  called  standard.  The  simplest 
classification  is  that  by  which  wrought  iron  is  divided  into  two 
large  classes  according  to  the  method  by  which  it  is  made. 
Wrought  iron  made  from  charcoal  pig  iron  is  named  charcoal 
iron.  This  is  usually  refined  and  double-refined  by  the  methods 
that  will  be  described  later  in  this  chapter.  Wrought  iron  made 
from  coke  pig  iron  is  known  as  common  iron. 

According  to  a  second  classification,  wrought  iron  is  graded 
into  four  different  grades  or  qualities:  i.  Norway  or,  more 
correctly,  Swedish  iron,  which  is  very  fibrous  and  used  for  the 
best  class  of  work.  This  is  made  from  pig  iron  produced  from 
magnetite  ore,  low  in  phosphorus,  and  with  charcoal  as  fuel  in 
the  blast  furnace.  Although  it  is  frequently  referred  to  as  Nor- 
way iron,  this  wrought  iron  comes  from  Sweden,  the  well-known 
Dannemora  iron  being  one  of  the  best  grades  known.  This 
iron  is  unusually  free  from  sulphur  and  phosphorus,  both  of 


68  IRON  AND   STEEL 

which  elements  have  an  injurious  effect  upon  the  metal,  sulphur 
making  the  iron  red-short,  that  is,  brittle  when  hot,  and  phos- 
phorus making  it  cold-short,  that  is,  easily  broken  when  cold. 
2.  Double-refined  or  best-refined  iron,  which  is  the  best  American 
domestic  iron  and  which  is  used  generally  in  forging,  welding, 
and  machine  work.  3.  Refined  iron,  which  is  a  good  grade  of 
domestic  wrought  iron.  4.  Common  iron,  which  is  made  either 
from  pig  iron  or  from  wrought-iron  scrap.  This  quality  does 
not  weld  as  easily  as  the  other  grades. 

According  to  still  another  system  of  classification,  wrought 
iron  is  graded  into  three  classes  —  charcoal  iron,  puddle  iron, 
and  busheled  scrap  iron.  Charcoal  iron,  as  the  name  indicates, 
is  made  from  charcoal  pig  iron.  Puddle  iron  is  the  second  grade, 
made  from  a  good  quality  of  coke  pig  iron.  The  puddle  iron,  in 
turn,  is  divided  into  either  three  classes,  A,  B,  and  C>  or  into 
staybolt  iron  and  merchant  iron.  The  busheled  scrap  iron  is  made 
from  wrought-iron  scrap  which  frequently  contains  pieces  of 
steel;  hence,  it  is  not  uniform,  does  not  weld  as  readily  as  the 
other  grades,  and  is  not  as  reliable. 

British  wrought  iron  is  classified  according  to  its  origin,  as 
Yorkshire  and  Staffordshire  iron.  The  Yorkshire  iron  is,  in  turn, 
classified  as  Lowmoor  and  Farnley  iron.  The  Yorkshire  iron  is 
the  best  British  quality  of  wrought  iron  produced,  and  is  made  in 
large  quantities.  The  Staffordshire  iron  is  of  a  lower  grade  and 
the  demand  for  it  is  constantly  decreasing  on  account  of  mild 
steel  being  substituted  for  it.  The  best  Yorkshire  iron  costs 
about  twice  as  much  as  low-grade  Staffordshire  iron. 

Corrosion  of  Wrought  Iron.  —  Wrought  iron  resists  corrosion 
to  a  remarkable  degree.  At  Delhi,  in  India,  there  is  a  monu- 
mental column  made  from  wrought  iron  which  is  more  than 
one  thousand  years  old,  and  in  various  other  parts  of  India, 
where  the  climate  is  exceptionally  humid,  iron  made  by  the 
natives  centuries  ago  is  still  in  existence  fully  exposed  to  the 
climatic  conditions.  In  England,  there  are  some  exposed 
wrought-iron  hand-rails  at  the  Epping  church,  near  London, 
which  are  one  hundred  and  fifty  years  old.  The  iron  used  in 
all  of  these  cases  was  probably  smelted  with  charcoal  as  a  fuel, 


WROUGHT  IRON  69 

puddled  in  small  quantities,  and  by  the  use  of  high-grade  ore; 
hence,  the  wrought  iron  would  be  of  exceptionally  high  quality. 

Peculiarities  of  Wrought  Iron.  —  If  a  i-inch  bar  of  the  best 
Yorkshire  iron  is  nicked  |  inch  deep  all  around,  say,  with  a 
sharp  set,  and  is  then  broken  over  the  anvil  with  a  single  blow, 
the  bar  will  break  square.  The  fracture  will  be  coarsely  granular, 
resembling  badly  burnt  steel,  but  the  granular  structure  will 
be  coarser.  A  bar  nicked  on  only  one  side,  and  carefully  bent 
with  the  nick  a  couple  of  inches  from  the  edge  of  the  vise  or  anvil, 
will  show  a  gray  silky  fibrous  structure,  free  from  crystals.  The 
reason  for  this  peculiarity,  which  is  found  only  in  the  best  York- 
shire iron,  has  never  been  satisfactorily  explained. 

The  lower  grades  of  wrought  iron  make  an  apparent  weld  at 
almost  a  melting  temperature  as  well  as  at  low  heat.  With  the 
better  grades  of  iron,  however,  a  heat  between  closer  limits  of 
temperature  is  necessary;  hence,  good  wrought  iron  should  be 
worked  only  by  a  competent  blacksmith,  who  must  give  closer 
attention  to  his  work  than  when  handling  the  cheaper  grades. 
The  less  the  iron  is  worked  at  the  weld,  the  better  will  be  the 
job.  Unnecessarily  working  a  weld  at  a  comparatively  low  heat, 
so  as  to  make  a  good-looking  job,  may  reduce  the  total  strength 
of  the  weld  several  tons  per  square  inch. 

Manufacture  of  Wrought  Iron.  —  In  the  manufacture  of 
wrought  iron,  the  processes  used  differ  slightly  according  to  the 
kind  of  wrought  iron  being  made  and  the  raw  materials  from 
which  it  is  produced.  As  common  wrought  iron  may  be  made 
either  from  pig  iron  or  from  scrap,  it  will  be  necessary  to  refer 
to  the  methods  used  in  either  case.  Refined  wrought  iron  is 
made  by  melting  pig  iron  and  puddling  it  in  a  puddling  furnace 
in  the  same  way  as  common  iron,  but  the  resulting  product,  in 
the  form  of  bars,  is  subjected  to  a  second  heating  and  re-rolling, 
thus  producing  what  is  known  as  "refined"  iron.  Double-re- 
fined iron  passes  through  the  same  processes  as  refined  iron,  but 
the  bars  thus  obtained  are  again  cut  up,  reheated  and  re-rolled. 
The  double  rolling  of  the  metal  makes  it  very  fibrous,  and  this 
kind  of  material  is  extensively  used  in  the  construction  of  passen- 
ger and  freight  cars,  because  of  its  ductility  and  its  capacity  for 


70  IRON  AND   STEEL 

withstanding  shocks  and  vibrations,  in  which  regard  it  is  much 
superior  to  steel.  Sometimes  the  molten  blast-furnace  metal  is 
charged  directly  into  the  puddling  furnace,  but,  as  a  rule,  pig 
iron  is  used  as  the  raw  material  for  wrought  iron.  The  pig 
iron  from  which  wrought  iron  is  made  generally  contains  from 
3  to  5  per  cent  of  carbon.  As  the  carbon  in  wrought  iron  ordi- 
narily does  not  exceed  0.25  per  cent  and  generally  is  much  lower 
than  this,  the  excess  of  carbon  must  be  removed  during  the 
puddling  process. 

Making  Common  Wrought  Iron  from  Pig  Iron.  —  The  pig  iron 
which  is  the  raw  material  for  making  wrought  iron  is  melted  in 
a  so-called  "puddling"  furnace  where  most  of  the  silicon,  carbon, 
phosphorus,  and  other  impurities  contained  in  the  pig  iron  are 
separated  from  it,  forming  the  puddle  cinder.  One  type  of 
puddling  furnace  is  shown  diagrammatically  in  the  sectional 
and  plan  view  in  the  accompanying  illustration.  The  fuel  is 
placed  on  the  grate  bars  at  A  and  the  metal  on  the  hearth  at  B. 
The  hot  gases  of  combustion  pass  over  the  bridge  wall  C  and  are 
deflected  against  the  metal  by  the  sloping  roof  D;  then,  passing 
over  the  rear  bridge  wall  E,  they  go  up  the  chimney  F.  Some- 
times the  hearth  is  made  with  a  long  slope  toward  the  rear 
bridge  wall  and  the  pigs  are  piled  upon  this  slope.  As  the  iron 
melts,  it  runs  into  the  depression  at  the  center  of  the  hearth 
where  it  is  collected  for  "  puddling. "  As  pig  iron  melts  at  about 
2100  degrees  F.  and  wrought  iron  at  about  2700  degrees  F.,  the 
temperature  in  the  puddling  furnace  is  so  gaged  that  it  is  high 
enough  to  melt  the  pig  iron,  but  not  high  enough  to  keep  wrought 
iron  in  a  liquid  state.  Therefore,  as  soon  as  the  small  particles 
of  iron  become  purified  they  partly  congeal  or  "come  to  nature," 
forming  a  spongy  mass  in  which  small  globules  of  iron  are  in  a 
semi-plastic  state. 

Previous  to  this  stage  being  reached,  the  impurities  in  the 
iron  have  been  reduced  in  three  stages.  Most  of  the  silicon  and 
manganese  and  some  of  the  phosphorus  are  removed  in  the  "melt- 
ing" stage;  more  of  the  phosphorus  and  some  of  the  sulphur  are 
removed  in  the  "clearing"  stage;  and  the  oxygen  and  most  of  the 
remaining  phosphorus  and  sulphur  are  removed  in  the  "boiling" 


WROUGHT  IRON 


stage.  The  purer  the  iron,  the  higher  is  its  melting  point,  so 
that,  as  the  molten  iron  is  purified,  it  naturally  becomes  pasty. 
When  this  pasty  condition  is  reached,  the  iron  is  puddled  or 
stirred  by  long  rods  for  about  an  hour.  During  this  time  the 
carbon  and  other  impurities  are  oxidized  by  coming  constantly 
in  contact  with  the  oxygen  of  the  air.  The  carbon  monoxide 
that  is  liberated  burns  in  jets  of  blue  flame  known  as  "pud- 
dlers'  candles. "  At  this  stage,  the  slag  begins  to  sink  or  "drop, " 
and  granules  of  wrought  iron  gradually  increasing  in  size  appear 
on  the  surface  of  the  metal  as  it  congeals  or  "  comes  to  nature. " 


Machinery 


Sectional  View  of  Puddling  Furnace 

The  objects  of  the  agitation  or  " puddling,"  which  is  accom- 
plished chiefly  by  a  long  rod  called  a  " rabble"  which  the  puddler 
introduces  through  a  notch  in  the  furnace  door,  and  which  is 
assisted  by  the  boiling  of  the  metal,  are  (i)  to  produce  as  uniform 
conditions  as  possible  throughout  the  bath;  (2)  to  break  up  the 
larger  masses  of  iron  that  tend  to  form;  and  (3)  to  prevent,  as 
far  as  possible,  the  settling  of  the  iron  in  a  partly  refined  condi- 
tion on  the  relatively  cold  bottom.  The  more  fluid  the  metal, 
the  more  active  must  be  the  agitation,  and  the  finer  will  be  the 
grain  of  the  resulting  iron. 

When  puddled,  the  mass  is  divided  by  the  puddler  into  pud- 
dle balls  or  lumps  of  about  from  60  to  100  pounds  each.  The 


72  IRON    AND    STEEL 

balls  or  lumps  formed  by  the  puddler  are  shaped  into  elongated 
blooms  in  a  rotary  squeezer,  and  while  still  hot  are  rolled  out 
into  bars  known  as  "  muck  bars."  In  American  practice,  these 
bars  are  from  3  to  6  inches  wide,  f  inch  thick,  and  from  15  to 
30  feet  long;  their  size  compares  with  the  size  of  the  bloom 
in  the  ratio  of  about  8  or  9  to  i.  The  muck  bars  are  now  cut 
into  pieces  of  from  one  to  four  feet  (in  American  practice  gener- 
ally 3^  feet)  in  length,  and  are  stacked  in  piles  varying  in  weight 
from  100  to  2000  pounds.  These  piles  are  placed  in  a  reheating 
furnace,  and  when  white  hot  are  taken  to  the  rolls  to  be  rolled 
out  and  welded  together.  At  this  time,  the  wrought  iron  may 
be  rolled  into  bars,  sheets,  plates,  or  structural  shapes.  The 
second  rolling  produces  a  more  uniform  material.  When  cold, 
this  material  is  sheared  and  straightened,  and  is  then  ready  for 
the  market. 

After  leaving  the  puddling  furnace,  wrought  iron  does  not 
undergo  any  material  change  in  its  chemical  composition,  and 
the  only  physical  change  is  an  expulsion  of  a  large  portion  of 
the  cinder;  the  small  cinder-coated  globules  of  iron  are  welded 
together,  and  the  subsequent  rolling  back  and  forth  elongates 
these  globules,  giving  the  iron  a  fibrous  structure,  and  the  re- 
heating and  re-rolling  drive  these  fibers  closer  together,  thus  in- 
creasing the  strength  and  ductility  of  the  metal. 

The  work  of  making  wrought  iron  by  the  puddling  process  sub- 
jects the  puddler  to  severe  physical  strain.  He  is  exposed  to 
intense  heat,  and  at  the  same  time  must  perform  hard  physical 
labor  in  stirring  and  moving  the  heavy  lumps  of  iron.  Ma- 
chines have  been  devised  for  doing  this  work,  but  have  not  been 
successful,  and  it  is  still  performed  in  a  manner  very  similar  to 
that  in  which  it  has  been  done  for  centuries. 

Making  Common  Wrought  Iron  from  Scrap.  — Common 
wrought  iron  may  be  made  from  wrought-iron  scrap  composed 
of  old  horseshoes,  bolts,  bars,  etc.  Frequently  this  scrap  also 
contains  pieces  of  steel,  but  this  lowers  the  quality  of  the  product. 
The  scrap  is  piled  together  and  put  into  a  heating  furnace  where 
it  is  heated  to  a  white  heat  —  a  heat  high  enough  to  temporarily 
hold  the  pieces  of  scrap  together.  It  is  then  run  through  rolls 


WROUGHT  IRON  73 

and  formed  into  flat  bars  which  are  cut  up  into  the  required 
lengths,  three  bars  being  placed  together  to  form  the  sides  and 
bottom  of  what  is  known  as  a  "box,"  temporarily  held  together 
by  U-shaped  irons.  Scrap  iron  is  now  put  into  this  box  and 
another  bar  is  placed  on  top  to  complete  the  box,  after  which  the 
sides  of  the  box  are  fastened  together  with  iron  bands.  These 
boxes  which  are  known  either  as  "box-piles"  or  as  "faggots" 
are  stacked  up  into  large  piles,  usually  by  placing  four  in  one 
direction  and  four  crosswise  in  another  direction.  These  piles 
are  heated  to  a  white  heat  in  the  furnace  and  then  each  box-pile 
is  passed  through  the  rolls  to  make  the  finished  wrought  iron. 
As  the  flat  bars  forming  the  sides  of  the  pile  have  been  rolled 
once,  they  have  a  denser  grain  than  the  center,  which  is  com- 
posed of  the  scrap  iron  that  has  not  been  rolled  before.  The 
finished  bars,  therefore,  have  a  fairly  good  surface,  but  they  are 
not  homogeneous,  and  scrap  wrought  iron  is  not  as  good  as  that 
made  directly  from  pig  iron  by  the  puddling  process.  Fur- 
thermore, as  the  scrap  material  is  not  uniform  in  quality,  the 
quality  of  the  product  varies.  Common  wrought  iron  made 
from  scrap  is  also  known  as  "busheled  iron."  It  should  not 
be  used  when  a  first-class  product  is  required. 

Other  Processes  for  Making  Wrought  Iron.  —  In  addition  to 
the  puddling  process,  there  are  several  processes,  known  as 
charcoal-hearth  processes,  in  which  the  wrought  iron  is  made  by 
methods  somewhat  different  from  those  used  in  puddling.  One 
of  these  is  the  "finery"  process,  which  is  employed  for  making 
the  best  Yorkshire  iron.  Another  is  the  "Walloon"  process, 
which  is  employed  in  Sweden  for  making  wrought  iron  from 
Dannemora  pig  iron,  and  a  third  is  the  "Lancashire"  process, 
which  is  also  principally  used  in  Sweden,  but  also  to  some  extent 
in  the  United  States.  The  highest  grade  of  wrought  iron  is 
made  by  the  charcoal-hearth  process,  although  the  puddling 
process  is  by  far  the  most  common  method  and  produces  the 
largest  quantities  of  wrought  iron.  The  essential  difference 
between  the  two  processes  is  that,  in  the  charcoal-hearth  method, 
atmospheric  air  supplies  the  oxygen  for  oxidation,  and  the  fuel 
is  burnt  in  contact  with  the  iron,  while  in  the  puddling  process 


74  IRON  AND   STEEL 

the  chief  source  of  oxygen  is  magnetic  oxide  of  iron,  and  the  fuel 
is  burnt  in  a  separate  chamber  from  that  containing  the  iron. 

Manufacture  of  Yorkshire  Wrought  Iron.  —  Yorkshire  wrought 
iron  is  manufactured  by  a  process  known  as  the  "dry"  process, 
similar  in  some  respects  to  the  puddling  process,  as  described, 
but  previous  to  applying  this  process,  the  pig  iron  is  subjected 
to  a  special  treatment.  The  process,  which  was  introduced 
over  a  hundred  years  ago,  is  now  infrequently  used  except  for 
the  class  of  iron  mentioned.  In  this  process,  only  white  pig 
iron  is  employed.  In  order  that  the  charge  for  the  charcoal- 
hearth  furnace  shall  be  uniform,  the  pigs  are  first  placed  in  a 
" refinery"  furnace,  in  which  the  pig  iron  is  first  melted  down  in 
a  coke  or  charcoal  fire  in  order  to  remove  the  silicon,  phosphorus, . 
and  sulphur,  and  to  change  what  graphitic  carbon  may  be  present 
into  the  combined  form.  The  metal  is  then  transferred  in  a 
molten  condition  to  the  charcoal-hearth  furnace,  after  which 
the  process  proceeds  as  follows:  The  furnace  is  charged  with 
damp  charcoal  and  a  low-pressure  unheated  blast  is  used,  the 
metal  being  puddled  in  a  similar  manner  as  in  the  puddling  fur- 
nace, to  make  all  parts  of  it  come  in  contact  with  the  blast. 
The  puddling  proceeds  for  about  an  hour,  the  same  as  in  the 
puddling  furnace,  after  which  the  metal  is  formed  into  balls 
and  treated  the  same  as  puddled  iron.  In  some  cases,  the  iron 
and  slag  are  tapped  out  of  the  furnace  together,  instead  of  being 
fed  directly  to  the  puddling  furnace,  the  iron  solidifying  in  molds 
in  the  form  of  thin  slabs  which  are  sprayed  with  water  to  quicken 
the  cooling,  and  which  are  then  broken  up  and  charged  into  the 
charcoal-hearth  furnace. 

The  Walloon  Process.  —  In  the  Walloon  process,  a  charcoal 
fire  is  used  into  which  long  pigs  are  gradually  pushed,  so  that 
they  slowly  melt  on  the  forward  end.  As  the  iron  melts,  it  falls 
drop  by  drop  through  the  blast  and  collects  in  a  pasty  mass 
at  the  bottom  of  the  furnace.  When  dropping  through  the 
blast,  it  is  decarburized.  The  pasty  iron  mass,  which  is  partially 
refined,  is  then  raised  to  the  top  of  a  charcoal  fire,  where  it  is 
melted  in  the  presence  of  slag  and  hammer  scale.  From  this 
point  on  the  process  resembles  that  of  the  puddling  process. 


WROUGHT  IRON  75 

Lancashire  Process.  —  In  the  Lancashire  process,  the  pig  iron 
is  melted  between  two  layers  of  charcoal,  and  as  the  iron  becomes 
liquid  it  drops  down  through  the  blast  and  is  decarburized  in 
a  manner  similar  to  that  of  the  Walloon  process,  the  molten 
metal  collecting  in  a  pasty  mass  at  the  bottom  of  the  furnace. 
After  having  remained  there  for  from  twenty  minutes  to  half 
an  hour,  it  is  melted  down  with  hammer  scale  and  slag  the 
same  as  in  the  Walloon  process. 

Defects  in  Wrought  Iron.  —  The  principal  defects  of  wrought 
iron  are  rough  places,  "spilly"  places,  blisters,  and  excess  of 
slag.  Rough  places  are  due  to  careless  workmanship,  imperfec- 
tion in  the  rolls,  and  red-shortness.  Spilly  places  are  spongy 
or  irregular  spotted  parts,  and  are  particularly  noticeable  in 
sheets,  although  sometimes  present  in  all  kinds  of  wrought  iron; 
they  are  generally  attributed  to  imperfect  puddling.  Any  im- 
purities that  may  be  present  in  wrought  iron  also  greatly  influ- 
ence its  properties.  Silicon  tends  to  produce  hardness  and 
brittleness,  and  if  0.35  per  cent  is  present,  the  iron  will  be  cold- 
short and  deficient  in  strength.  Phosphorus  also  will  render  it 
cold-short,  if  0.25  per  cent  is  present.  If  0.03  per  cent  of  sulphur 
is  present,  red-shortness  is  caused. 

Testing  Wrought  Iron.  —  In  testing  wrought  iron,  the  tensile 
strength  varies  according  to  whether  the  iron  is  tested  "with" 
or  "across"  the  grain;  that  is,  "with"  or  "across"  the  direction 
of  rolling.  In  testing  steel,  this  condition  need  not  be  considered, 
as  the  strength  in  either  direction  is  practically  equal.  The 
strength  of  wrought  iron  in  bending  or  flexure  also  varies  ac- 
cording to  whether  the  bending  is  "  with"  or  "  across"  the  grain. 
Wrought  iron  is  tested  in  a  number  of  different  ways  in  order 
to  determine  not  only  its  strength,  but  its  forging  qualities  and 
other  characteristics.  The  United  States  Navy  Department 
specifies  that  it  should  be  possible  to  bend  wrought  iron  cold  to 
an  angle  of  180  degrees  over  a  diameter  of  one  thickness.  In 
addition,  it  is  subjected  to  tests  for  tensile  strength,  elongation, 
and  reduction  of  area,  as  well  as  "  nick"  and  "  drift"  tests.  The 
nick  test  consists  in  nicking  the  bar  approximately  20  per  cent  of 
its  thickness  and  bending  it  back  at  this  point  to  an  angle  of 


76  IRON  AND   STEEL 

1 80  degrees.  It  must  then  show  a  clean  fiber,  free  from  slag  and 
dirt,  and  free  from  any  coarse  crystalline  spots.  A  few  crystal- 
line spots  may  be  tolerated,  provided  they  do  not,  in  the  aggre- 
gate, exceed  10  per  cent  of  the  sectional  area  of  the  bar.  The 
drift  test  consists  in  punching  and  expanding  the  bar  by  pointed 
drifts  until  a  round  hole  is  formed,  the  diameter  of  which  is  not 
less  than  0.9  of  the  diameter  of  the  rod  or  the  width  of  the  bar. 
Any  indication  of  fracture,  cracks,  or  flaws  developed  by  this 
test  will  cause  the  rejection  of  the  material. 

Ram's-horn  Test.  —  The  so-called  "ram's-horn"  test  was  com- 
monly applied  in  past  years,  and  is  still  used  in  many  places. 
It  is  a  satisfactory  test  for  indicating  the  forging  qualities  of 
wrought  iron.  To  make  this  test,  a  hole  about  one  and  one- 
quarter  times  the  size  of  the  bar  or  the  thickness  of  the  plate 
to  be  tested  is  drifted  hot  from  the  solid,  leaving  the  same  dis- 
tance clear  from  the  end  or  the  side.  When  testing  a  bar,  the 
metal  between  the  hole  and  the  end  of  the  bar  is  then  split  with 
a  sharp  set  from  both  sides  and  turned  over  sideways.  The 
name  of  the  test  is  derived  from  the  appearance  of  the  test  piece 
after  this  bending  has  taken  place.  Bars  up  to  a  sectional  area 
of  about  two  square  inches  may  be  tested  in  one  heat,  but  larger 
sections  require  two  heats,  and  frequently  two  heats  are  used  for 
smaller  sections  also,  in  which  case  a  second  hole  of  the  same  size 
as  the  first  is  drifted  lower  down  the  bar  at  right  angles  to  the 
first.  When  flat  plates  are  tested,  one  horn  is  turned  sideways 
and  the  other  forward.  When  cold,  the  test  specimen  should 
show  no  defects  and  the  surface  of  the  ram's-horns  should  be 
free  from  cracks.  It  is  necessary  to  use  a  clean  fire  and  con- 
siderable speed  in  performing  this  test,  as  otherwise  the  metal 
may  be  injured  by  the  manipulation,  although  it  is  of  good  qual- 
ity otherwise. 

Tests  on  Iron  for  Different  Purposes.  —  Boiler  plate  should  be 
subjected  to  tensile  tests,  hot  and  cold  bending  tests,  and  hot 
drifting  tests.  Wrought  iron  for  rivets  should  be  subjected  to 
tensile  tests,  hot  and  cold  bending  tests,  and  upsetting  tests. 
Staybolt  iron  should  be  subjected  to  an  endurance  test  by  thread- 
ing the  ends  of  an  8-inch  specimen  and  fixing  one  end  while  the 


WROUGHT  IRON  77 

other  end  is  revolved  in  a  circular  path  fy  inch  in  diameter. 
While  revolving,  the  iron  should  be  stressed  with  a  tensile  stress 
of  4000  pounds  per  square  inch,  and  should  then  be  capable  of 
making  at  least  6000  revolutions  without  cracking  or  breaking. 
Wrought-iron  wire  is  tested  by  tension,  bending,  and  torsion 
tests.  The  bending  tests  are  made  in  a  hand  vise  the  jaws  of 
which  have  a  radius  of  curvature  equal  to  twice  the  diameter  of 
the  wire.  The  quality  of  the  metal  is  shown  by  the  number 
of  times  that  it  can  be  bent  without  cracking  or  breaking. 

Tests  Indicating  Quality  of  Iron.  —  The  reduction  of  area  is 
the  typical  test  that  determines  more  accurately  than  any  other 
the  real  quality  of  wrought  iron  and  hence  bears  a  direct  relation 
to  its  price.  The  best  Yorkshire  bar  iron  has  been  known  to 
have  a  reduction  of  area  of  60  per  cent,  and  usually  exceeds  50 
per  cent,  while  ordinary  wrought  iron  seldom  has  a  reduction  of 
area  as  high  as  30  per  cent.  Two  grades  of  wrought  iron  may 
have  approximately  the  same  tensile  strength  and  the  same 
percentage  of  elongation,  but  the  reduction  of  area  will  indicate 
which  is  the  better  quality. 

Specifications  for  Wrought  Iron.  —  Two  grades  of  wrought 
iron  are  specified  by  the  U.  S.  Navy  Department.  Wrought 
iron  of  the  best  quality  required  for  naval  use  should  have  a 
minimum  tensile  strength  of  48,000  pounds  per  square  inch; 
a  minimum  elongation  of  26  per  cent;  and  a  minimum  reduction 
of  area  of  40  per  cent.  It  is  further  specified  that  the  phos- 
phorus content  must  not  exceed  o.i  per  cent,  nor  the  sulphur 
content  0.015  per  cent.  For  ordinary  blacksmith-shop  use,  the 
Navy  Department  requires  wrought  iron  having  a  minimum 
tensile  strength  of  45,000  pounds  per  square  inch;  a  minimum 
elongation  of  25  per  cent;  and  a  minimum  reduction  of  area  of 
40  per  cent  for  round  bars,  and  35  per  cent  for  flat  shapes.  The 
phosphorus  content  must  not  exceed  0.15  per  cent,  nor  the  sul- 
phur content  more  than  0.02  per  cent. 

Wrought-iron  Chain.  —  One  of  the  most  important  uses  for 
wrought  iron,  at  the  present  time,  and  one  to  which  no  other 
material  lends  itself  as  well,  is  for  the  making  of  chain.  The 
reason  for  this  is  two-fold:  In  the  first  place,  it  is  possible  to 


78  IRON  AND   STEEL 

weld  wrought  iron  with  the  assurance  of  obtaining  a  better  weld 
than  any  other  material,  and,  second,  good  wrought  iron,  when 
overstressed,  gives  warning  by  yielding  or  elongating,  before  it 
actually  breaks.  A  well-made  chain,  when  subjected  to  a  ten- 
sile test,  does  not  break  at  the  weld,  but  always  at  the  end  of  the 
link  that  is  not  welded,  or  at  the  side.  A  break  at  the  weld  in- 
dicates lack  of  skill  or  carelessness  in  the  production  of  the  chain. 
Chain  that  is  made  from  the  best  quality  of  iron  stiffens  when 
subjected  to  a  breaking  stress,  so  that  it  becomes  practically 
solid,  like  a  piece  of  bar  iron.  Chain  made  from  common  wrought 
iron  does  not  show  this  peculiarity;  hence,  it  may  be  used  as  a 
test  of  the  quality  of  the  iron  in  the  chain.  Any  chain  which, 
when  in  use,  indicates  a  lack  of  freedom  of  movement  has  been 
overstressed,  and  should  not  be  used. 

Difference  between  Wrought  Iron  and  Low-carbon  Steel.  — 
While  chemically  there  is  not  much  difference  between  wrought 
iron  and  low-carbon  steel,  there  is  considerable  difference  in 
their  physical  structures.  Owing  to  the  globules  of  pure  iron 
being  coated  with  cinder  in  the  puddling  furnace,  the  subsequent 
rolling  and  reworking,  while  expelling  a  large  portion  of  this 
cinder,  always  leaves  a  trace  of  it  behind  which  gives  wrought 
iron  the  fiber.  As  steel  is  produced  in  a  liquid  form  and  the 
cinder  floats  to  the  top  and  is  removed,  the  metal  is  without  any 
grain  or  fiber.  When  subjected  to  many  vibrations,  or  strains 
due  to  frequent  expansion  and  contraction,  wrought  iron  will 
generally  yield  gradually  and  give  warning,  while  steel  is  more 
liable  to  snap  off  suddenly.  The  fibers  of  wrought  iron  can  break 
one  at  a  time  without  directly  affecting  its  neighbor  (like  the 
strings  in  a  rope),  but  if  a  rupture  is  once  started  in  steel,  it  will 
extend  more  rapidly. 

Wrought  iron  will  also  resist  corrosion  and  pitting  longer  than 
steel,  no  doubt  due  to  the  higher  resisting  power  of  the  enclosed 
cinder,  which  also  causes  the  acid  to  deflect  endwise,  thus  weak- 
ening its  action  by  diffusing  it  over  a  larger  area  and  preventing 
deep  pitting.  Staybolts  and  boiler  tubes  for  locomotives  have 
proved  more  satisfactory  when  made  of  wrought  iron  than  of 
steel.  Thin  sheets,  tin  plate,  corrugated  iron  covering,  wire 


WROUGHT  IRON  79 

fencing,  pipes,  oil-well  casings,  etc.,  have  also  proved  much  more 
durable  when  made  of  wrought  iron  than  when  made  of  steel. 
On  the  other  hand,  in  rails,  tires,  guns,  armor  plate,  etc.,  steel 
has  proved  far  superior  to  iron,  owing  to  its  greater  strength 
and  hardness;  corrosion  is  also  here  of  minor  importance,  owing 
to  the  rails,  etc.,  generally  being  worn  out  long  before  corrosion 
has  a  chance  to  affect  them  seriously.  When  structural  steel  or 
iron  is  used  for  bridges,  etc.,  it  is  necessary  to  protect  the  metal 
from  serious  corrosion  by  frequent  and  careful  painting;  in  the 
skeletons  of  high  office  buildings  and  other  sky-scrapers,  when 
completely  covered  with  concrete,  etc.,  so  as  to  thoroughly  ex- 
clude air  or  moisture,  steel  as  well  as  iron  will  probably  last  indefi- 
nitely. Where  material  is  buried  in  the  ground,  or  exposed  to 
the  weather  without  the  careful  protection  of  paint,  or  where 
moisture  has  access  to  it  by  other  channels,  as  in  the  interior  of 
of  pipes,  wrought  iron  will  outlast  steel  by  a  good  margin. 

Open-hearth  Iron.  —  Some  manufacturers  are  offering  "  open- 
hearth  iron"  as  a  substitute  for  wrought  iron,  and  claim  certain 
properties,  such  as  resistance  to  corrosion,  etc.  Open-hearth 
iron  is  made  in  the  open-hearth  furnace  at  a  high  temperature, 
and  is,  therefore,  considerably  overheated  in  the  manufacture. 
When  used  in  the  form  of  sheets,  this  overheating  is  probably 
rectified  in  the  subsequent  annealing,  but,  in  bars,  the  material 
possesses  a  coarse  structure  and  shows  what  is  known  as  a 
" fiery  fracture."  The  working  temperature  of  open-hearth 
iron  is  comparatively  limited.  It  must  be  worked  at  a  compara- 
tively high  heat  which  produces  the  coarse  crystalline  structure. 
When  the  temperature  falls  below  this  point,  the  iron  is  brittle 
and  is,  therefore,  not  susceptible  to  mechanical  working.  Open- 
hearth  iron  should  not  be  used  as  a  substitute  for  wrought  iron, 
except  for  sheets  and  other  parts  where  final  annealing  of  the 
material  is  possible.  A  sample  of  this  iron  was  found  to  con- 
tain 0.07  per  cent  of  carbon;  0.03  per  cent  of  manganese;  0.006 
per  cent  of  phosphorus;  and  0.02  per  cent  of  sulphur. 

Specifications  for  substitutes  for  wrought  iron  have  been 
issued  by  the  U.  S.  Navy  Department,  which  for  certain  pur- 
poses permits  the  use  of  extra  soft  steel  instead  of  wrought  iron, 


8o  IRON  AND   STEEL 

requiring,  however,  that  the  phosphorus  content  in  such  steel 
must  not  exceed  0.04  per  cent;  the  sulphur  content  must  not 
exceed  0.04  per  cent;  and  the  carbon  content  must  not  exceed 
o.i  2  per  cent.  The  specifications  further  require  a  minimum 
tensile  strength  of  45,000  pounds  per  square  inch  and  a  maxi- 
mum tensile  strength  of  55,000  pounds,  with  a  minimum  elon- 
gation of  28  per  cent,  and  a  minimum  reduction  in  area  of  48  per 
cent.  The  elongation  for  rods  or  bars  J  inch  in  diameter  or  less 
is  measured  on  a  length  equal  to  eight  times  the  diameter  or  the 
thickness  of  the  section  tested.  Sections  over  \  inch,  but  less 
than  f  inch,  in  diameter  or  thickness,  are  measured  on  a  length 
of  6  inches,  and  sections  above  f  inch,  in  diameter  or  thickness, 
are  measured  on  a  length  of  8  inches.  The  elastic  limit  must  not 
be  less  than  one-half  the  ultimate  strength  of  any  specimen. 
The  steel,  when  scarf -welded  and  subjected  to  a  cold  bending 
test  at  the  center  of  the  weld,  consisting  in  being  bent  flat  to  180 
degrees,  must  not  show  either  cracks  or  flaws  on  the  outer  curve 
of  the  bend. 

Distinguishing  Wrought  Iron  from  Steel.  —  Wrought  iron  may 
be  distinguished  from  soft  steel  by  cleaning  it  of  scale  and  grease 
and  immersing  it  for  from  15  to  20  minutes  in  a  mixture  consist- 
ing of  3  parts  of  sulphuric  acid  and  i  part  of  muriatic  acid,  mixed 
with  nine  parts  of  water.  The  acids  are  poured  into  the  water, 
and  the  mixture  allowed  to  cool  before  it  is  used.  After  the 
sample  is  removed  from  this  solution,  it  should  be  rinsed  with 
water.  The  fibrous  structure  of  the  wrought  iron  should  then  be 
apparent;  as  steel  has  a  crystalline  structure,  it  will  dissolve 
uniformly  and  show  no  fiber.  Most  wrought  iron  can  also  be 
distinguished  from  steel  quite  easily  when  turning  or  planing  it, 
on  account  of  the  fibrous  structure. 


CHAPTER  V 
CLASSIFICATION  AND   CHARACTERISTICS  OF  STEEL 

STEEL  may  be  defined  as  an  alloy  of  iron  and  carbon,  together 
with  small  percentages  of  a  number  of  other  elements,  such  as 
manganese,  silicon,  sulphur,  and  phosphorus.  So-called  "  spe- 
cial" or  "  alloy"  steels  also  contain  small  percentages  of  some 
other  metal,  such  as  nickel,  chromium,  vanadium,  tungsten,  etc. 
According  to  the  definition  adopted  by  the  Brussels  Congress 
of  the  International  Association  for  Testing  Materials,  held  in 
1906,  steel  is  defined  as  "iron  which  is  malleable  at  at  least 
some  one  range  of  temperature,  and,  in  addition,  is  either  cast 
into  an  initially  malleable  mass,  or  is  capable  of  hardening 
greatly  by  sudden  cooling,  or  is  so  cast  and  so  capable  of  hard- 
ening." Originally,  the  term  " steel"  referred  only  to  what  is 
now  generally  known  as  high-carbon  steel  or  tool  steel,  which  pos- 
sesses, in  an  exceptionally  high  degree,  the  quality  of  hardening 
when  being  heated  to  a  certain  temperature  and  quenched  in  a 
cooling  bath.  Later,  when  the  open-hearth  and  Bessemer  proc- 
esses were  developed,  the  products  of  these  processes  were  also 
termed  "steel,"  although  a  Bessemer  or  open-hearth  steel  with 
a  comparatively  low  carbon  content  differs  in  its  properties  and 
general  characteristics  from  a  high-carbon  tool  steel  even  more 
than  a  low-carbon  or  mild  Bessemer  or  open-hearth  steel  differs 
from  wrought  iron.  Strictly  speaking,  therefore,  an  entirely  new 
term  ought  to  have  been  used  for  the  product  produced  by  the 
new  processes.  Those  who  developed  the  processes,  however,  were 
anxious  to  call  the  product  "  steel,"  and  so  this  name  has  been 
adopted  for  a  large  range  of  metal  having  carbon  contents  vary- 
;.ng  all  the  way  from  o.io  to  2.0  per  cent,  and  physical  character- 
istics so  different  as  to  suggest  entirely  different  metals. 

In  steel  which  does  not  contain  any  other  metal,  such  as  nickel, 
chromium,  tungsten,  etc.,  the  characteristic  element  which 

81 


82  IRON  AND  STEEL 

changes  its  properties  in  the  most  marked  way  is  carbon.  The 
amount  of  carbon  is  given  either  in  percentage  or  in  "points." 
A  point  is  a  one-hundredth  of  one  per  cent  of  the  whole  mass  of 
steel,  by  weight;  thus,  for  example,  a  3O-point  carbon  steel  con- 
tains 0.30  per  cent  of  carbon.  The  same  system  may  be  applied 
to  the  percentage  of  other  elements  present  in  the  steel;  for 
example,  a  steel  containing  3!  points  of  sulphur  would  be  a  steel 
having  a  sulphur  content  of  0.035  Per  cent. 

Classification  of  Steel.  —  There  are  a  great  many  different 
methods  according  to  which  steel  may  be  classified.  With 
regard  to  the  methods  of  production,  it  may  be  classified  as 
"crucible"  steel,  which  is  made  by  the  crucible  process;  " Bes- 
semer" steel,  which  is  made  by  the  Bessemer  process;  "open- 
hearth"  steel,  which  is  made  in  the  open-hearth  furnace;  and 
"electric"  steel,  which  is  made  in  the  electric  furnace.  With 
regard  to  the  carbon  content,  steel  may  be  classified  as  "mild" 
or  "low-carbon"  steel  —  sometimes  also  known  as  "machine" 
or  "machinery"  steel  —  which  does  not  harden  appreciably  when 
heated  and  suddenly  cooled,  and  which  generally  does  not  con- 
tain more  than  0.25  per  cent  of  carbon;  "medium"  steel,  which 
contains  from  0.30  to  0.60  per  cent  of  carbon,  and  which  becomes 
perceptibly  harder  by  being  heated  and  quenched,  but  which  is 
not  hard  enough  to  use  for  cutting  tools;  and  "high-carbon" 
steel,  which  contains  anywhere  from  0.65  to  1.55  per  cent  of 
carbon,  and  which  possesses  the  property  of  hardening  to  a 
marked  degree  when  heated  and  quenched.  This  steel  is  often 
termed  "tool  steel,"  because  of  being  suitable  for  cutting  tools, 
files,  etc.  There  is,  however,  no  distinct  line  of  demarkation 
between  these  different  varieties,  as  they  merge  gradually  into 
one  another.  Generally  speaking,  mild  and  medium  steels  are 
made  by  the  Bessemer  or  open-hearth  process,  while  high- 
carbon  steel  is  made  by  the  crucible  and  electric  processes. 
While  the  best  high-carbon  steel  is  made  by  the  latter  processes, 
it  is  possible  to  make  such  steel  by  either  of  the  other  proc- 
esses. In  general,  the  Bessemer  process  produces  the  cheaper 
grades  of  steel,  for  rails  and  structural  work.  Most  of  the 
steel  now  used  is  made  in  the  open-hearth  furnace  which  pro- 


CLASSES  OF  STEEL  83 

duces  a  better  grade  of  steel  than  the  Bessemer.  Open-hearth 
steel  is  used  for  boiler  plate,  bridge  work,  heavy  forgings,  etc. 
The  crucible  process  produces  a  still  higher  quality  of  steel  which 
is  used  for  tools,  small  forgings,  and  high-class  machine  parts. 
The  electric  process  is  a  competitor  of  the  crucible  process  in  the 
production  of  a  high  class  of  tool  steel,  and  the  former  is  also  used 
to  a  limited  extent  in  making  some  kinds  of  structural  steel. 
All  the  varieties  known  as  " steel"  differ  from  both  wrought  iron 
and  cast  iron  in  one  particular :  they  are  all  produced  in  a  molten 
condition  and  are  at  once  cast  into  ingots,  which  are  afterwards 
rolled  or  hammered.  Cast  iron  may  be  so  cast,  but  cannot  after- 
wards be  rolled,  while  wrought  iron  may  be  rolled,  but  not  cast. 

From  the  metallurgist's  point  of  view,  steel  may  also  be  clas- 
sified according  to  the  number  of  elements  besides  iron  that 
affect  its  characteristics.  Steel  is  then  divided  into  binary, 
ternary,  and  quaternary  alloys.  Binary  alloys  are  steels  that 
have  one  alloying  element  in  addition  to  iron;  since  carbon  is 
always  present  in  alloys  of  iron,  carbon  steel  is  the  typical 
binary  alloy.  Ternary  alloys  are  steels  that  have  two  alloying 
elements,  in  addition  to  iron.  Since  carbon  is  invariably  present, 
it  is  one  of  these  elements.  These  steels  take  their  name  from 
the  other  elements,  such  as  nickel  steel,  chromium  steel,  man- 
ganese steel,  etc.  The  alloying  elements  may  be  present  in  any 
desired  quantity.  Quaternary  alloys  are  steels  having  three 
alloying  elements,  in  addition  to  iron;  these  elements  may  be 
present  in  any  proportion.  Carbon  being  one  of  these,  the  other 
two  are  shown  by  the  name  of  the  steel;  thus,  chrome-nickel 
steel,  silico-manganese  steel,  etc. 

With  regard  to  the  use  for  which  steel  is  intended,  it  may  be 
classified  in  many  different  ways,  and  a  number  of  terms  have 
become  so  thoroughly  accepted  in  the  iron  and  steel  trade  as  to 
constitute  distinct  names  for  steels.  Among  these  may  be 
mentioned:  Flange  steel,  machine  steel,  magnet  steel,  spring 
steel,  structural  steel,  etc. 

Steel  may  also  be  classified  as  " carbon  steel"  and  " alloy 
steel,"  according  to  whether  carbon  or  some  other  element  has 
the  greatest  influence  upon  its  characteristics.  All  steel  in  which 


84  IRON  AND   STEEL 

the  carbon  content  is  the  chief  factor  in  determining  its  charac- 
teristics is  known  as  carbon  steel.  Alloy  steels,  or  special  steels, 
are  those  which  contain  some  other  metal  besides  carbon,  which 
gives  them  some  peculiar  characteristic  not  possessed  by  ordinary 
carbon  steel.  Among  the  most  important  alloy  steels  are: 
Tungsten  (also  frequently  known  as  "  high-speed ")  steel,  chro- 
mium steel,  nickel  steel,  vanadium  steel,  and  titanium  steel. 

When  steel  is  melted  in  a  furnace  and  cast  in  molds  in  a  man- 
ner similar  to  that  in  which  cast-iron  castings  are  made,  the 
product  is  known  as  " steel  castings."  The  term  "cast  steel" 
should  not  be  used  in  this  connection,  because  cast  steel  originally 
was  used  to  designate  crucible  steel,  and  while  the  term  is  now 
obsolete  and  little  used,  it  is  better  to  use  the  term  "  steel  cast- 
ings" rather  than  "cast  steel,"  when  steel  cast  in  molds  is  re- 
ferred to.  Semi-steel  is  another  grade  of  steel  melted  and  cast 
in  molds.  It  is  produced  by  melting  together  cast  iron  with 
wrought  iron  or  soft  steel  scrap. 

Definitions  of  Terms  used  to  Designate  Steel.  —  The  follow- 
ing alphabetical  arrangement  contains  brief  definitions  of  the 
most  important  names  that  are  applied  to  different  kinds  of  steel, 
and  to  steel  used  for  different  purposes: 

Air-hardening  steel  is  a  tool  steel  containing,  in  addition  to 
carbon,  an  element  such  as  tungsten,  so  that  the  steel  will 
harden  by  simply  cooling  in  the  air  or  by  inserting  the  healed 
end  in  an  air  blast. 

Alloy  steel  is  a  steel  the  properties  of  which  depend  princi- 
pally upon  some  element  other  than  carbon,  such  as  nickel, 
tungsten,  chromium,  etc. 

Bessemer  steel  is  a  steel  of  any  carbon  content  made  by  the 
Bessemer  process. 

Blister  steel  is  steel  produced  by  impregnating  bars  of  wrought 
iron 'or  soft  steel  with  carbon,  by  heating  them  in  contact  with 
carbonaceous  matter. 

Carbon  steel  is  steel  which  owes  its  properties  chiefly  to 
various  percentages  of  carbon;  it  is  known  as  " carbon  steel" 
to  distinguish  it  from  steels  containing  other  elements  which 
chiefly  control  the  physical  properties. 


CLASSES  OF  STEEL  85 

Cast  steel  is  the  same  as  crucible  steel;  the  term  "cast  steel" 
is  confusing  and  little  used. 

Cement  steel  is  steel  which  is  made  by  the  cementation  or 
converting  process  and  is  the  same  as  blister  steel. 

Chrome  or  chromium  steel  is  an  alloy  steel  usually  containing 
about  from  0.30  to  2  per  cent  of  chromium. 

Converted  steel  is  the  same  as  blister  steel. 

Crucible  steel  is  steel  made  by  the  crucible  process,  irrespective 
of  the  carbon  content.  It  is  sometimes  called  "cast  steel," 
and,  in  England,  "pot  steel." 

Damascus  steel  was  formerly  made  at  Damascus  by  some 
direct  process;  the  steel  was  covered  with  beautiful  designs  and 
used  principally  for  sword  blades  and  gun  barrels. 

Electric  steel  is  steel  produced  in  an  electrically-heated  furnace. 

Flange  steel  is  a  steel  of  such  quality  that  it  may  be  bent  cold 
for  forming  flanges  on  sheets,  etc. 

Fluid  compressed  steel  is  steel  which  has  been  subjected  to 
compression  before  the  ingots  were  entirely  solidified,  in  order 
to  secure  a  perfectly  solid  and  homogeneous  mass. 

High-speed  steel  is  a  term  frequently  applied  to  alloy  steels, 
owing  to  the  fact  that  metal-cutting  tools  made  from  them  may 
be  run  at  high  speeds  without  losing  their  temper  or  hardness. 

Machine  or  machinery  steel  is  a  steel  containing  about  0.20 
per  cent  of  carbon/and  is  intended  primarily  for  casehardening. 

Magnet  steel  is  a  term  applied  to  tungsten  steel  when  used  for 
permanent  magnets. 

Manganese  steel  is  steel  usually  containing  from  n  to  14  per 
cent  of  manganese. 

Molybdenum  steel  is  a  steel  having  properties  which  are 
quite  similar  to  those  of  tungsten  steel. 

Nickel  steel  is  a  steel  usually  containing  from  3  to  5  per  cent 
of  nickel. 

Open-hearth  steel  is  a  steel  made  by  the  open-hearth  process, 
irrespective  of  its  carbon  content. 

Puddled  steel  is  a  slag-bearing  steel  made  by  the  puddling 
process,  which  contains  enough  carbon  to  harden,  when  sud- 
denly cooled;  it  is  rarely,  if  ever,  made  at  the  present  time. 


86  IRON  AND   STEEL 

Saniter  steel  is  a  steel  made  by  the  Saniter  desulphurizing 
process. 

Self-hardening  steel  is  the  same  as  air-hardening  steel. 

Semi-steel,  which  is  used  for  making  "semi-steel  castings,"  by 
melting  about  from  one-third  to  one-fifth  (by  weight)  of  wrought 
iron  or  soft  steel  scrap  with  cast  iron,  usually  in  a  cupola,  is  also 
known  as  " toughened  cast  iron." 

Shear  steel  is  steel,  usually  in  the  form  of  bars,  made  from 
blister  steel,  by  shearing  it  into  short  lengths,  arranging  in  piles, 
and  welding  these  piles  by  rolling  or  hammering  at  a  welding 
heat.  If  this  process  of  shearing,  etc.,  is  repeated,  the  product 
is  called  "double-shear  steel."  It  is  made  principally  in  Eng- 
land and  used  for  articles  of  cutlery,  etc. 

Siemens-Martin  steel  is  steel  made  by  the  open-hearth  process. 

Special  steels  are  steels  which  owe  their  properties  princi- 
pally to  an  element  or  elements  other  than  carbon.  These  are 
also  called  "alloy  steels." 

Spring  steel  is  a  steel  containing  from  0.80  to  i.oo  per  cent  of 
carbon,  suitable  for  making  springs. 

Steel  castings  are  unforged  and  unrolled  castings  made  from 
any  kind  of  steel,  whether  Bessemer,  open-hearth,  or  crucible. 

Structural  steel  is  a  grade  of  steel  suitable  in  composition 
and  shape  of  cross-section  for  structural  purposes,  and  made  in 
various  grades,  such  as  dead-soft  open-hearth;  soft  Bessemer; 
soft  open-hearth;  medium  open-hearth;  and  hard  open-hearth. 

Titanium  steel  is  a  steel  which  is  given  special  properties  by 
adding  small  percentages  of  titanium. 

Tool  steel  is  any  kind  of  high-carbon  steel  suitable  for  making 
cutting  tools. 

Tungsten  steel  is  steel  usually  containing  from  5  to  18  per 
cent  of  tungsten,  and  from  0.4  to  2.0  per  cent  of  carbon.  It  is 
extensively  used  for  high-speed  metal-cutting  tools. 

Vanadium  steel  is  steel  usually  containing  from  0.15  to  0.25 
per  cent  of  vanadium.  It  is  also  known  as  "anti-fatigue  steel," 
owing  to  its  unusual  capacity  for  resisting  repeated  stresses. 

Weld  steel  is  iron  containing  enough  carbon  to  harden  if  heated 
and  suddenly  cooled.  The  term  "wrought  steel"  is  also  used. 


CHARACTERISTICS  OF  STEEL  87 

Peculiarities  of  Steel.  —  If  heated  beyond  a  certain  tempera- 
ture, steel  becomes  burned  and  a  permanent  injury  is  done  to 
the  metal;  hence,  steel  must  be  worked  at  a  lower  temperature 
and  with  greater  care  than  wrought  iron.  For  this  reason,  welds 
in  steel  cannot  be  relied  upon  with  the  same  certainty  as  those 
in  wrought  iron,  and  the  higher  the  carbon  content,  the  less 
suitable  is  the  steel  for  welding.  Because  of  the  lack  of  relia- 
bility of  the  welds,  and  also  because  steel  is  likely  to  rupture 
more  suddenly  than  wrought  iron,  it  has  not  been  able  to  take 
the  place  of  wrought  iron  for  chain-making.  Steel  worked  at  a 
blue  or  black  heat  is  injured  more  than  if  strained  when  cold. 
This  property  is  known  as  "blue  shortness."  Steel  is  also 
affected  by  such  action  as  shearing  or  punching,  so  that  it  is 
preferable  to  drill  holes  in  steel  plates  rather  than  to  punch  them. 
The  crushing  stress  exerted  upon  the  edge  of  the  plate  in  shear- 
ing has  been  found  to  have  greater  effect  upon  the  quality  of  the 
metal  in  the  case  of  steel  than  in  the  case  of  wrought  iron. 

Effect  of  Method  of  Working  on  Strength  of  Steels.  —  The 
strength  of  a  steel  depends  upon  the  manner  of  working  it  as 
well  as  upon  its  chemical  composition.  If  steel  is  not  thor- 
oughly worked  it  will  be  soft,  weak,  and  not  very  tough.  A 
plate  2  inches  thick  is  not  as  strong  and  tough,  proportionately, 
as  a  plate  J  inch  thick,  because  the  thinner  plate  is  much  more 
thoroughly  worked.  Excessive  working,  on  the  other  hand, 
lessens  the  ductility.  For  instance,  the  strength  of  a  steel  may 
be  about  doubled  by  drawing  it  into  wire,  but  the  ductility  will 
be  reduced  to  a  very  small  fraction  of  i  per  cent.  When  steel 
is  "cold  drawn"  or  "cold  rolled,"  as  the  process  is  frequently 
although  erroneously  called,  its  tensile  strength  may  be  in- 
creased as  much  as  from  20  to  40  per  cent  and  its  elastic  limit 
from  60  to  100  per  cent;  but  its  elongation  is  reduced.  By  this 
process  the  steel  is  given  a  hard  skin  or  shell,  but  the  core  is 
unchanged. 

If  the  steel  contains  a  large  proportion  of  carbon,  the  manner 
of  cooling  after  working  will  also  have  a  very  important  effect. 
Sudden  cooling  or  "hardening"  has  an  effect  similar  to  that  of 
cold  working.  The  amount  of  the  effect  will  depend  upon  the 


88  IRON  AND   STEEL 

proportion  of  carbon  present,  the  temperature  from  which  it  was 
cooled,  the  temperature  to  which  it  is  cooled,  and  the  length  of 
time  in  which  the  cooling  takes  place. 

Distinguishing  Various  Kinds  of  Steel  by  Mechanical  Tests. 
-  The  best  way  to  determine  the  quality  and  composition  of  steel 
is  by  chemical  analysis  and  by  microscopic  inspection.  These 
methods,  however,  are  not  available  except  in  cases  where  a 
properly  equipped  laboratory  is  at  hand.  A  number  of  simple 
methods  may,  however,  be  used  to  determine  the  quality  of 
steel  with  fair  accuracy  for  general  purposes.  The  simplest  way 
to  distinguish  between  high-carbon  and  mild  steel  is  by  the  ap- 
pearance of  a  fresh  break.  High-carbon  steel  has  a  very  fine 
smooth  fracture,  while  the  fracture  of  soft  steel  is  rough  and 
coarse.  When  a  bar  of  high-carbon  steel  is  broken,  the  fracture 
is  nearly  silver-white,  while  the  fracture  of  low-carbon  steel  is 
more  gray  in  appearance.  If  a  bar  of  high-carbon  steel  and  a 
bar  of  mild  steel  are  nicked  all  around  and  then  placed  on  the 
anvil  with  the  nick  directly  over  the  edge  of  the  anvil,  the  bar 
of  high-carbon  steel  will  break  at  the  nick  when  struck  once  or 
twice  with  a  sledge,  but  a  bar  of  mild  steel  will  require  several 
blows  before  it  breaks. 

If  tools  are  hardened  after  being  forged  at  the  anvil  without 
any  preliminary  machining  or  grinding,  the  manner  in  which  the 
piece  " scales"  after  hardening  is  an  indication  of  its  quality. 
When  heated  to  a  cherry  red,  steel  containing  i  per  cent  of  carbon 
will  "scale  off"  evenly  and  leave  a  clean  surface.  Steel  con- 
taining 0.75  per  cent  of  carbon  will  scale  off  in  spots,  leaving  a 
kind  of  speckled  surface.  Low-carbon  steel  will  not  scale  off  at 
all,  unless  heated  to  a  very  bright  cherry  red  or  almost  yellow. 

Recognizing  Steels  by  Their  Sparks.  —  In  a  paper  read  before 
Copenhagen  Congress  of  the  International  Association  for 
Testing  Materials,  Max  Bermann  called  attention  to  the  fact 
that  the  sparks  given  off  when  grinding  iron  and  steel,  by  means 
of  emery  wheels,  present  a  different  appearance  according  to  the 
kind  of  material  ground.  The  path  of  the  spark  from  its  origin 
to  its  extinction  forms  a  line  of  light  which,  at  the  end,  branches 
out  in  every  direction,  having  an  explosion-like  appearance. 


CHARACTERISTICS  OF  STEEL 


89 


This  line  of  light  may  be  called  the  " spark  ray."  It  is  the  ends 
of  these  rays  that,  in  particular,  vary  for  different  classes  of 
steel,  and  which  in  the  following  will  be  called  the  "  spark  pic- 
tures. "  Some  of  these  spark  pictures  contain  only  a  very  few 
lines,  while  others  contain  a  great  many,  some  of  them  presenting 
secondary  explosions  and  projections,  as  if  they  were  suddenly 
thrown  out  in  various  directions  by  an  internal  force. 

With  a  carbon  content  of  from  0.07  to  0.08  per  cent,  the  number 
of  the  lines  in  the  spark  picture  is  from  two  to  three.  With 
an  increase  of  the  percentage  of  carbon,  the  number  of  the 
branching  lines  also  increases.  At  low  carbon  contents,  the  lines 


Machinery 


Fig.  i.    Spark  Pictures  obtained  from  Different  Kinds  of  Steel 

appear  to  start  from  different  points  of  the  drop  formation  at 
the  end  of  the  ray,  but  when  the  carbon  content  is  0.25  or  0.27 
per  cent,  the  lines  spring  from  a  common  point  of  the  drop  for- 
mation. The  larger  the  carbon  content  the  greater  is  the  crowd- 
ing of  the  lines  projecting  from  the  end  of  the  ray,  as  shown  at  A 
in  Fig.  i.  In  the  case  of  tool  steel,  the  spark  picture  resembles 
the  branch  of  a  blossom,  and  the  individual  branching  lines  have 
a  lilac-like  form. 

The  spark  picture  of  steel  containing  manganese  (as  illustrated 
at  B)  shows  at  the  end  of  the  individual  branching  lines  a  sec- 

6F 


90  IRON  AND   STEEL 

ondary  explosion-like  phenomenon,  shorter  lines  collecting  like 
leaves  around  a  common  central  point.  The  number  of  the 
primary  branching  lines  in  this  case  also  is  in  proportion  to  the 
carbon  percentage  in  the  steel;  the  extent  and  shape  of  the 
spreading  ends  of  the  primary  branching  lines  appear  to  be  in  a 
certain  relation  to  the  percentage  of  manganese  contained  by  the 
material. 

The  spark  rays  of  steel  containing  tungsten  (as  shown  at  C) 
are  dark  red  lines,  the  ends  of  which  show  no  spark  picture  if  the 
emery  wheel  is  not  sufficiently  sharp  and  the  pressure  between 
the  wheel  and  steel  is  small.  Only  the  very  end  of  the  ray  has 
a  broader  and  more  brightly  glowing  appearance,  indicating 
the  beginning  of  a  spark  picture.  If  the  steel  is  pressed  more 
firmly  against  the  wheel,  branching  lines  spring  out  in  an  ex- 
plosion-like manner.  These  lines,  however,  take  the  form  of 
small  shining  pin-head-like  balls.  The  spark  sheave  (a  combina- 
tion of  spark  rays  and  spark  pictures)  of  chrome-tungsten  high- 
speed steel  is  distinct  from  that  of  the  tungsten  steel  by  the  fact 
that  two  kinds  of  rays  appear,  some  very  thin  dark  red  and 
some  thicker  brighter  red  ones,  which  are  absent  in  the  regular 
tungsten  steel.  The  spark  pictures  consist  solely  of  short  curved 
drop  forms. 

The  spark  picture  of  nickel  steel,  containing  less  than  3  per 
cent  of  nickel,  is  identical  with  that  of  carbon  steel  with  a  cor- 
responding percentage  of  carbon.  In  case  of  larger  percentages 
of  nickel,  however,  the  nickel  steel  can  readily  be  .recognized 
by  the  aid  of  the  spark  test,  because  the  spark  pictures  show  them- 
selves in  a  sporadic  manner,  whereas,  in  the  case  of  carbon  steel; 
they  occur  in  close  proximity  and  in  close  succession  to  one  an- 
other. Diagram  D  illustrates  molybdenum  steel. 

Dark  gray  cast  iron  is  characterized  by  fine  dark  red  spark- 
rays,  spark  pictures  here  and  there,  and  lines  collecting  around 
the  drop  formation  like  a  net.  The  net-like  lines  disappear  more 
and  more  with  the  increase  of  assimilated  carbon,  and  with 
light  gray  cast  iron  they  disappear  altogether. 

Application  of  Spark  Test.  —  By  means  of  the  spark  test, 
different  kinds  of  steel  may  be  classified  according  to  their  carbon 


CHARACTERISTICS   OF   STEEL 


92  IRON  AND   STEEL 

percentage  and  according  to  the  metals  principally  alloyed  with 
them.  The  ends  of  rods  that  may  have  been  wrongly  arranged 
on  the  storing  racks  may,  for  example,  be  placed  against  a  re- 
volving emery  wheel  and  the  rods  thus  identified.  The  appli- 
cation of  this  method  in  the  inspection  of  received  material  affords 
a  rapid  test  for  making  sure  that  the  material  complies  with  the 
requirements.  The  test  also  supplies,  in  the  hands  of  an  ex- 
perienced observer,  a  sensitive  means  of  ascertaining  differences 
in  chemical  composition  at  different  places  of  the  same  bar  or 
piece  of  material,  it  being  possible  to  apply  this  test  to  both  steel 
and  cast  iron.  In  the  hardening  room,  by  means  of  the  spark 
test,  it  is  possible  to  determine  before  hardening  what  grade  and 
class  of  steel  has  been  used  for  making  the  various  tools,  so  that 
the  proper  hardening  process  may  be  applied.  In  the  forge  shop, 
the  method  may  be  of  value  for  determining  with  certainty  good 
malleable  wrought  iron. 

In  Fig.  2  are  shown  eight  different  spark  pictures.  These 
were  originally  shown  in  a  paper  presented  before  the  Indiana 
section  of  the  Society  of  Automotive  Engineers,  by  John  F. 
Keller.  At  A  is  shown  a  spark  picture  of  wrought  iron.  The 
branching  or  forking  of  the  luminous  sparks  indicates  the  pres- 
ence of  carbon.  At  B  is  shown  a  spark  picture  of  mild  steel, 
indicating  a  greater  percentage  of  carbon  than  that  present  in 
wrought  iron.  At  C  is  shown  a  spark  picture  of  iron  containing 
from  0.50  to  0.85  per  cent,  while  at  D  is  shown  the  spark  picture 
of  a  high-carbon  tool  steel.  The  spark  picture  shown  at  E 
results  from  high-speed  steel ;  at  F,  a  spark  picture  of  manganese 
steel;  at  G,  one  of  Mushet  steel;  and  at  H,  one  produced  by 
special  magnet  steel. 

Determining  the  Hardness  of  Steel.  —  The  hardness  of  steel 
and  other  metals  may  be  determined  by  the  sclerometer,  the 
scleroscope,  the  Brinell  indentation  test,  and  the  drill  test. 
In  the  sclerometer  test,  a  weighted  diamond  point  is  drawn,  once 
forward  and  once  backward,  over  the  smooth  surface  of  the 
material  to  be  tested.  The  hardness  number  is  the  weight, 
in  grams,  required  to  produce  a  "standard  scratch,"  which  is 
one  that  is  just  visible  to  the  naked  eye  as  a  dark  line  on  a  bright 


CHARACTERISTICS  OF  STFFL  93 

reflecting  surface.  It  is  also  the  scratch  that  can  just  be  felt 
with  the  edge  of  a  quill  when  the  latter  is  drawn  over  the  smooth 
surface  at  right  angles  to  a  series  of  such  scratches  produced  by 
regularly  increasing  weights. 

In  the  scleroscope  test,  a  small  steel  cylinder,  with  a  hardened 
point  and  weighing  about  40  grains,  is  allowed  to  fall  upon  the 
smooth  surface  of  the  metal  to  be  tested;  the  height  of  the  re- 
bound of  the  hammer  is  taken  as  the  measure  of  hardness.  The 
height  of  the  rebound  of  hardened  steel  is  in  the  neighborhood 
of  100  on  the  scale,  or  about  6J  inches,  and  the  total  fall  is  about 
10  inches,  or  254  millimeters. 

In  the  Brinell  test,  a  hardened  steel  ball  is  pressed  into  the 
smooth  surface  of  the  metal  so  as  to  make  an  indentation  of  such 
size  as  can  be  conveniently  measured  under  the  microscope. 
The  spherical  area  of  the  indentation  being  calculated  and  the 
pressure  being  known,  the  stress  per  unit  of  area  when  the  ball 
comes  to  rest  is  calculated,  and  the  hardness  number  obtained. 
Within  certain  limits,  the  value  obtained  is  independent  of  the 
size  of  the  ball  and  of  the  amount  of  pressure.  The  standard 
diameter  of  the  ball  is  (10  millimeters  (0.3937  inch)  and  the 
pressure,  3000  kilograms  (6615  pounds)  in  the  case  of  iron  and 
steel;  for  softer  metals,  a  pressure  of  500  kilograms  (1102  pounds) 
is  used.  Of  late,  Brinell  instruments  have  been  so  constructed 
that  the  microscope  is  not  required. 

In  the  Keep  drill  test,  a  standard  steel  drill  is  caused  to  make 
a  definite  number  of  revolutions  while  it  is  pressed  with  standard 
force  against  the  specimen  to  be  tested.  The  hardness  is  auto- 
matically recorded  on  a  diagram  on  which  a  dead  soft  material 
gives  a  horizontal  line,  while  a  material  as  hard  as  the  drill  itself 
gives  a  vertical  line,  intermediate  hardness  being  represented 
by  the  corresponding  angle  between  o  and  90  degrees. 

Comparison  of  Hardness  Testing  Methods.  —  Each  form  of 
test  has  its  advantages  and  its  limitations.  The  sclerometer 
is  cheap,  portable,  and  easily  applied,  but  the  test  is  not 
applicable  to  materials  that  do  not  possess  a  fairly  smooth 
leflecting  surface,  and  the  standard  scratch  is  only  definitely 
recognized  after  some  experience. 


94  IRON  AND   STEEL 

The  scleroscope  test  is  simple,  rapid,  and  definite  for  materials 
for  which  it  is  suited,  but  the  results  obtained  vary  somewhat 
with  the  size  and  thickness  of  the  sample.  As  a  comparative 
measure  of  the  hardness  of  material  of  the  same  quality  and 
structure,  it  is  quite  accurate,  but  it  is  not  reliable  for  comparing 
the  hardness  of  two  different  metals. 

The  Brinell  test  is  especially  useful  for  structural  materials. 
It  is  definite  and  easily  applied,  but  it  cannot  be  applied  to  very 
brittle  materials,  such  as  glass,  nor  is  it  satisfactory  for  use  on 
hardened  high-carbon  steel.  For  materials  for  which  it  is  suited, 
the  Brinell  test  also  has  the  advantage  that  it  may  be  used  as  a 
measure  of  the  ultimate  strength  of  the  material.  But  there  is 
no  definite  relation  between  hardness,  as  measured  by  the  Brinell 
hardness  testing  method,  and  wear.  While,  in  general,  a  high 
Brinell  hardness  number  may  be  expected  to  indicate  a  metal 
that  will  give  better  wear,  there  are  so  many  exceptions  that  this 
test  for  indicating  wearing  properties  would  be  unreliable.  For 
instance,  Hadfield's  manganese  steel,  which  has  a  low  Brinell 
hardness  number,  is  one  of  the  best  steels  as  far  as  wear  is  con- 
cerned. 

The  Keep  drill  test  is  especially  suited  for  castings  of  all 
kinds,  as  it  records  not  only  the  surface  hardness,  but  also  the 
hardness  of  the  whole  thickness,  and  gives  indications  of  blow- 
holes, hard  streaks,  and  spongy  places.  Obviously,  it  cannot 
be  applied  to  materials  too  hard  to  be  conveniently  drilled  by  a 
hardened  steel  drill. 

Microscopic  Study  of  Steel.  —  The  study  of  the  appearance 
of  steel  under  the  microscope,  showing  what  is  known  as  the 
microstructure  of  steel  has  become  one  of  the  most  important 
methods  in  studying  the  properties  of  steel,  as  well  as  other 
metals.  The  science  of  the  microstructure  of  metal  is  known  by 
metallurgists  as  metallography.  By  means  of  this  microscopic 
study  of  steel,  it  is  possible  for  the  experienced  metallurgist 
to  determine  many  things  relating  to  the  composition  and  char- 
acteristics of  steel.  The  magnified  surface  reveals  the  tem- 
perature at  which  steel  has  been  hardened  or  tempered,  and,  in 
casehardened  steel,  the  depth  to  which  the  hardness  has  pene- 


CHARACTERISTICS  OF  STIll.L  95 

trated.  The  carbon  content  can  be  closely  judged  when  the 
steel  is  in  the  annealed  state.  The  quantity  of  special  alloying 
metals  that  are  added  to  steel,  such  as  nickel,  chromium,  tung- 
sten, etc.,  can  also  be  estimated.  The  microscopic  examination 
also  shows  flaws  and  imperfections  in  the  metal,  and  indicates 
the  mechanical  treatment  to  which  it  has  been  subjected,  whether 
rolled,  forged,  slowly  pressed  into  shape,  or  cast.  In  many 
cases,  the  microscopic  study  of  steel  shows,  to  the  experienced 
observer,  the  various  properties  of  iron  and  steel  for  industrial 
purposes  which  a  chemical  analysis  would  fail  to  reveal. 

Method  of  Performing  Microscopic  Examination.  —  If  a 
specimen  of  steel  is  to  be  examined  under  the  microscope,  it 
must  first  be  properly  prepared  for  this  purpose.  Steel  as  it 
leaves  the  manufacturer  may  be  in  a  number  of  different  states 
as  regards  its  microstructure.  In  order  to  study  it  under  the 
microscope  it  should  first  be  annealed  by  being  heated  to  about 
1800  degrees  F.  and  cooled  very  slowly.  The  different  constitu- 
ents will  then  appear  in  what  is  called  the  normalized  state.  A 
flat  surface  is  then  formed  upon  the  specimen  by  filing  or  grind- 
ing, and  this  surface  is  then  polished  with  successive  grades  of 
abrasives  until  a  mirror-like  polish  is  obtained.  This  surface  is 
then  etched  with  a  suitable  acid  or  etching  reagent  in  order  to 
reveal  clearly  the  structure  of  the  metal  when  the  specimen  is 
examined  under  the  microscope.  The  etching  acid  acts  un- 
equally upon  the  different  constituents,  turning  some  darker 
than  others,  so  that  they  can  be  readily  distinguished  under  the 
microscope.  The  acid  also  cuts  away  certain  of  the  constituents, 
making  other  parts  stand  out  in  relief.  These  raised  portions 
resemble  hills  or  plateaus  in  miniature  and  show  white  from 
the  reflected  light  in  the  microscope;  the  portions  that  are  cut 
away  are  valleys  that  receive  no  light,  and,  therefore,  appear  black. 

Sometimes  an  etching  acid  or  reagent  is  used  that  will  color 
some  of  the  constituents,  so  that  they  may  be  distinguished  by 
their  color.  The  basis  of  the  three  most  commonly  used  etching 
reagents  are  picric  acid,  nitric  acid,  and  tincture  of  iodine. 
The  picric  acid  reagent  is  prepared  as  follows:  Five  grains  of 
picric  acid  are  dissolved  in  95  cubic  centimeters  of  absolute 


96  IRON   AND   STEEL 

alcohol,  and  the  specimen  to  be  etched  is  immersed  in  this 
solution  for  30  seconds.  The  nitric  acid  reagent  is  prepared  by 
mixing  10  parts  of  nitric  acid  with  90  parts  of  alcohol.  The 
specimen  is  immersed  in  this  solution  for  from  10  to  15  seconds. 
Tincture  of  iodine  is  used  as  a  reagent  by  spreading  one  drop  on 
each  square  centimeter  of  surface  to  be  etched,  and  allowing 
it  to  remain  on  the  surface  until  the  specimen  is  discolored. 

One  of  the  constituents  of  steel,  known  as  "cementite"  (re- 
ferred to  in  detail  later) ,  is  not  as  easily  attacked  by  the  ordinary 
etching  reagents  as  the  other  constituents,  and,  therefore,  a 
different  etching  reagent  is  used.  An  immersion  for  30  minutes 
in  a  2-per-cent  solution  of  oxalate  of  ammonium  will  give  a  red 
color  to  cementite,  and  a  picrate  of  soda  solution  will  give  it  a 
brown  color. 

In  addition  to  the  etching  method  for  preparing  the  specimen, 
some  specimens  are  prepared  by  "  polishing  in  relief,"  which  is 
done  with  a  piece  of  parchment  stretched  over  a  smooth  pine 
block.  Rouge  is  rubbed  firmly  into  the  parchment  and  the 
latter  is  then  rinsed  over  with  running  water  so  that  only  the 
rouge  is  left  that  has  been  forced  into  the  pores  of  the  parchment. 
The  specimen  to  be  tested  is  now  rubbed  over  this  soft  surface, 
by  means  of  which  the  softer  elements  in  the  specimen  are 
ground  out  below  the  level  of  the  harder  elements.  In  this  way, 
the;  harder  elements  which  stand  out  will  show  white,  while  the 
softer  elements  that  are  ground  out  will  show  darker.  A  third 
method,  known  as  "  polish  attack,"  which  is  a  combination  of 
the  etching  and  polishing  method,  is  also  used.  In  this  method 
a  pine- wood  block  is  covered  with  parchment  the  same  as  in  the 
relief  polishing  method,  but,  instead  of  using  rouge,  the  parch- 
ment is  dampened  with  a  solution  of  2  parts  of  crystallized  nitrate 
of  ammonium  in  98  parts  of  water.  The  specimen  is  then  rubbed 
upon  the  parchment  until  the  etching  reagent  has  properly 
etched  the  surface. 

When  the  regular  etching  reagents  are  used,  the  specimen  to 
be  etched  is  placed  in  a  small  porcelain  receptacle  just  large 
enough  to  permit  covering  the  specimen  with  the  etching  acid, 
which  latter  should  be  thrown  away  after  being  used  once.  Be- 


CHARACTERISTICS  OF  STEEL  97 

for  immersing  the  specimen  in  the  etching  solution,  the  sur- 
face to  be  etched  must  be  perfectly  clean  and  free  from  any 
trace  of  grease.  It  is  also  important  that  the  etching  solution 
comes  in  contact  with  every  part  of  the  surface  to  be  etched 
immediately,  as  otherwise  uneven  and  possible  misleading  effects 
may  be  obtained.  Grease  is  most  easily  removed  by  washing 
the  specimen  before  immersion  with  a  dilute  solution  of  caustic 
soda  or  caustic  potash,  or  with  ether. 

As  soon  as  the  specimen  has  been  etched,  it  is  washed  at  once 
by  rinsing  in  water  or  in  alcohol,  ether,  or  chloroform,  in  order 
to  remove  all  trace  of  the  etching  reagent.  After  washing,  the 
specimen  may  be  quickly  dried  with  a  piece  of  cloth,  or,  if  al- 
cohol or  some  other  volatile  liquid  has  been  used  for  the  washing, 
the  specimen  may  be  dried  by  allowing  a  current  of  warm  air  to 
play  upon  the  surface.  This  latter  method  is  especially  desir- 
able, because  it  insures  that  the  etched  surface  is  not  disturbed 
by  the  rubbing  of  the  cloth. 

Constituents  of  Steel  as  Revealed  by  Microscope. —  A  piece 
of  low-carbon  steel  containing  about  0.12  per  cent  of  carbon 
prepared  as  described  would  appear  under  the  microscope  about 
as  shown  in  Fig.  3.  The  dark  grains  are  called  pearlite.  The 
white  background  is  called  ferrite,  and  consists  principally  of 
iron  with  a  few  impurities.  In  fact,  ferrite  may  be  considered 
as  pure  iron,  and  when  carbon  is  added  to  it,  each  atom  of 
carbon  absorbs  or  combines  with  three  atoms  of  iron.  This 
carbide  of  iron  is  called  cementite.  Pearlite,  again,  is  an  intimate 
.mixture  of  cementite  and  ferrite  in  the  definite  proportion  of 
32  parts  of  ferrite  to  5  parts  of  cementite;  hence,  referring  to 
Fig.  3,  it  will  be  seen  that  a  piece  of  low-carbon  steel,  treated  as 
mentioned,  consists  of  a  white  background  of  iron  or  ferrite 
interspersed  with  a  number  of  dark  grains  which  consist  also  of 
some  ferrite  or  iron  in  laminations  or  layers  separated  by  lami- 
nations of  carbide  of  iron  or  cementite,  the  combination  of 
ferrite  and  cementite,  as  mentioned,  being  termed  pearlite. 
In  Fig.  4  is  shown  a  steel  containing  0.42  per  cent  of  carbon 
treated  in  the  same  way.  The  difference  is  quite  apparent. 
There  is  a  much  larger  number  of  dark  grains  of  pearlite,  due  to 


IRON  AND   STEEL 


Fig.  3.     Steel,  0.12  Per  Cent  Carbon;    Magnification,  300 


- 


Fig.  4.     Steel,  0.42  Per  Cent  Carbon;    Magnification,  300 


CHARACTERISTICS  OF   STEEL  99 

the  increase  of  carbon,  and  it  becomes  obvious  that  there  must 
be  a  steel  high  enough  in  carbon  content  to  be  composed  of  all 
dark  grains  and  have  little  or  no  white  background;  in  other 
words,  the  steel  is  composed  entirely  of  pearlite  without  any 
ferrite  background.  Such  a  condition,  in  fact,  is  reached  when 
the  steel  contains  from  0.80  to  0.90  per  cent  of  carbon,  and  steel 
of  this  kind  is  known  as  eutectoid  or  saturated  steel.  Below  this 
percentage,  the  surface  shows  pearlite  and  ferrite,  and  above  this 
percentage  of  carbon,  it  shows  pearlite  and  cementite.  All 
steel  with  a  lower  carbon  content  is  called  hypo-eutectoid  and  all 
steel  containing  more  than  from  0.80  to  0.90  per  cent  of  carbon 
is  called  hyper-eutectoid.  In  high  carbon  steel,  the  pearlite  and 
cementite  will  be  present  until  a  carbon  content  of  6.6  per  cent 
is  reached,  when  the  whole  structure  will  be  cementite.  Fig. 
5  shows  the  appearance  of  a  steel  containing  i  per  cent  of  carbon, 
showing  excess  of  carbide  of  iron  or  cementite  in  connection  with 
pearlite. 

Microscopic  Study  of  Heat-treated  Steels.  —  In  heat-treated 
steels,  the  ferrite,  pearlite,  or  cementite,  which  are  the  con- 
stituents of  annealed  or  normalized  steels,  are  replaced  by  other 
constituents.  It  is  for  heat-treated  steels  that  the  microscopic 
study  is  of  especial  value,  as  it  makes  it  possible  to  determine  the 
conditions  under  which  the  heat-treatment  has  been  conducted 
and  the  results  obtained.  Assume,  for  example,  that  a  piece  of 
normalized  steel  containing  the  required  amount  of  carbon  for 
hardening  is  heated  to  about  1500  degrees  F.  and  quenched  in 
water.  It  will  then  become  hardened.  If  polished,  etched,  and 
examined  under  the  microscope,  it  will  now  show  a  very  fine 
structure,  apparently  lacking  in  detail.  In  other  words,  the 
heat-treatment  has  caused  the  grains  to  become  merged  as  if  in 
a  solution  and,  as  a  matter  of  fact,  the  condition  is  referred  to 
by  that  name,  the  steel  being  said  to  be  in  a  state  of  solid  solu- 
tion. Heating  the  steel  to  the  temperature  mentioned  has 
allowed  the  solution  to  form,  and  the  sudden  cooling  has  arrested 
the  steel  in  this  condition.  The  constituent  obtained  in  a  steel 
that  has  been  heated  to  the  correct  hardening  temperature  and 
quenched  is  known  as  martensite.  While  the  steel  is  heated  above 


100 


IRON  AND  STEEL 


Fig.  5.    Steel,  i.oo  Per  Cent  Carbon;   Magnification,  too;  Note  Excess 
of  Carbide  of  Iron  or  Cementite 


Fig.  6.     Left:  Casehardened  Steel,  Core,  0.03  Per  Cent  of  Sulphur- 
Right:  0.06  Per  Cent  of  Sulphur 


CHARACTERISTICS  OF  STEEL  IOI 

the  temperature  required  for  hardening,  it  is  changed  to  aus- 
tenite,  but  does  not  remain  in  this  condition  when  subjected  to 
ordinary  heat-treatment.  If  the  steel  is  cooled  suddenly,  it 
changes  to  martensite  as  just  mentioned,  but  in  the  case  of  large 
pieces  of  steel,  the  center  is  not  affected  by  the  heat-treatment 
as  much  as  the  outer  portions,  and  another  constituent  known 
as  troostite,  usually  intermingled  with  martensite,  is  developed. 
The  martensitic  structure  of  hardened  steel  is  also  changed  into 
troostite  by  drawing  the  temper  by  reheating  to  a  temperature 
below  750  degrees  F.  Finally,  if  the  drawing  temperature  ex- 
ceeds 750  degrees,  a  constituent  called  sorbite  is  developed,  which 
reaches  its  maximum  at  about  noo  degrees  F.  Hardened  steels, 
the  temper  of  which  has  been  drawn  to  temperatures  between 
750  and  1 100  degrees  F.,  show  both  troostite  and  sorbite  and  are 
known  as  troosto-sorbitic  steels.  When  the  drawing  temperature 
does  not  reach  750  degrees  F.,  some  of  the  martensite  is  not 
transformed  into  troostite,  and  the  steel  is  known  as  troosto- 
martensitic  steel.  When  a  drawing  temperature  of  about  750 
degrees  F.  is  reached,  the  martensite  has  all  disappeared,  and  this 
condition  has  been  named  osmondite,  but  as  it  is  merely  the 
boundary  line  between  troostite  and  the  next  constituent  sor- 
bite, developed  by  the  higher  drawing  temperature,  it  is  doubt- 
ful if  any  definite  constituent  can  always  be  located  and  named 
in  this  manner.  If  steel  which  is  hot  enough  for  hardening  and 
is  in  the  austenitic  condition  is  cooled  slowly,  the  martensite 
which  is  trapped  or  fixed  by  sudden  cooling  is  not  retained,  but 
the  steel  finally  changes  back  to  pearlite  or  to  the  annealed  con- 
dition. 

Microscopic  Study  of  Casehardened  Steels.  —  If  a  piece  of 
low-carbon  steel  has  been  carburized  and  is  then  annealed  or 
normalized,  polished,  and  etched,  all  the  variations  of  carbon 
content  from  hypo-eutectoid  in  the  core  to  hyper-eutectoid  in 
the  outer  zone  or  case  may  be  noticed  by  microscopic  study. 
In  Fig.  7  is  shown  a  photo-micrograph  which  illustrates  a  por- 
tion of  a  casehardened  bar  from  the  outer  edge  inward,  almost 
through  the  depth  of  the  case.  The  outer  zone  is  hyper-eutec- 
toid, the  light  framework  being  cementite;  there  is  then  a 


102 


IRON  AND   STEEL 


Fig.  7.     Outer  Portion  of  Case;  Magnification,  50 


Fig.  8.     Continuation  of  Fig.  7  showing  Core 


CHARACTERISTICS  OF  STEEL  103 

eutectoid  zone  which  consists  of  pearlite  with  practically  no 
other  constituent;  and  finally  a  hypo-eutectoid  zone  which  con- 
sists of  pearlite  with  light  ferrite  grains.  The  illustration,  Fig. 
8,  is  a  continuation  towards  the  core  of  the  same  piece  as  shown  in 
Fig.  7,  the  light  white  line  at  the  bottom  of  Fig.  7  corresponding 
to  the  line  near  the  top  of  Fig.  8,  this  line  locating  the  two  photo- 
graphs with  relation  to  each  other.  If  the  two  photo-micro- 
graphs were  cut  along  these  two  white  lines  and  joined,  they 
would  make  a  continuous  view.  In  Fig.  8,  when  the  core  is 
reached,  the  ferrite  grains  predominate.  Incidentally,  Figs. 
7  and  8  show  an  example  of  a  specimen  which  represents  a  good 
carburization  process.  The  case  will  be  hard  when  heat-treated, 
and  will  adhere  well  to  the  core.  By  the  study  of  photo-micro- 
graphs such  as  those  referred  to,  valuable  information  as  to  the 
heat-treatment  being  given  to  steel  in  practical  work  may  be 
obtained. 

Fig.  6  shows  another  use  for  the  photo-micrograph.  Here, 
to  the  left,  is  shown  a  casehardened  steel  which  contains  0.03 
per  cent  of  sulphur;  to  the  right  is  shown  one  that  contains  0.06 
per  cent  of  sulphur.  The  effect  of  increasing  the  sulphur  con- 
tent is  very  apparent,  the  grain  being  very  much  coarser.  How- 
ever, with  the  present  knowledge  of  microscopic  examination  of 
iron  and  steel,  no  satisfactory  test  has  been  evolved  for  the  de- 
termination of  the  sulphur  content.  It  is  merely  possible  to  see 
the  difference  caused  by  different  amounts  of  sulphur.  The 
sulphur  and  phosphorus  content,  therefore,  should  be  deter- 
mined by  chemical  analysis. 

Photo-micrographs  of  Iron  and  Steel.  —  Figs.  9  to  32,  in- 
clusive, show  a  number  of  photo-micrographs  of  iron  and  steel 
containing  different  proportions  of  carbon,  and  having  been 
treated  in  different  ways.  Fig.  9  shows  a  low  carbon  specimen 
containing  about  0.05  per  cent  of  carbon;  here  ferrite  predomi- 
nates, with  small  areas  of  pearlite.  Fig.  10  shows  a  sample 
having  a  carbon  content  of  about  o.io  per  cent.  Figs,  n,  12, 
and  13  show  samples  with  increasing  carbon  percentages,  in- 
dicating also  an  increase  in  pearlite.  Fig.  14  shows  a  steel  having 
0.90  per  cent  of  carbon  in  which  the  pearlite  area  predominates. 


IO4 


IRON  AND   STEEL 


. 


Fig.  9.     Ferrite  and  Pearlite; 
Carbon,  0.05  Per  Cent 


Fig.  ii.     Ferrite  and  Pearlite; 
Carbon,  0.16  Per  Cent 


1 


Fig.  10.     Ferrite  with  Pearlite  Islands; 
Carbon,  o.io  Per  Cent 


Fig.  12.     Pearlite,  28  Per  Cent; 
Carbon,  0.25  Per  Cent 


"^H^^JP^' 

Fig.  13.     Pearlite,  60  Per  Cent;         Fig.  14.     Pearlite  Area  predominating; 
Carbon,  0.54  Per  Cent  Carbon,  0.90  Per  Cent 


CHARACTERISTICS   OF   STEEL 


Fig.  15.     Crucible  Steel 


Fig.  16.     Steel  in  Fig.  15,  Hot-rolled 


Fig.  17.     Steel  in  Fig.  16, 
Cold-drawn 


Fig.  18.     Steel  quenched  at  Correct 
Hardening  Temperature 


• 

1 


Fig.  19.  Steel  quenched  at  50  De-  Fig.  20.  Steel  quenched  at  100  De- 
grees C.  above  Correct  Hardening  grees  C.  above  Correct  Hardening 
Temperature  Temperature 


io6 


IRON    AND    STEEL 


Fig.  21.  Steel  quenched  at  200 
Degrees  C.  above  Correct 
Hardening  Temperature 


Fig.  22. 

Martensite  Structure  in  a  Fine- 
grained Steel 


Fig.  23.     Martensite  Structure  in  a 
Coarse-grained  Steel 


Fig.  24.     Troostite  Structure;  Steel 
drawn  at  250  Degrees  C. 


Fig.  25.    Temper  drawn  at  400  De- 
grees C.;    Osmondite  Structure 


Fig.  26.     Temper  drawn  at  550  De- 
grees C.;     Sorbite  Structure 


CHARACTERISTICS  OF   STEEL 


107 


Fig.  27.     Quenching  Oil  too  Hot; 
Troostite  and  Martensite  Structure 


Fig.  28.     Crystalline  Structure  of 
Overheated  Steel 


V-i 


v. 


V 


V 


Fig.  29.     Steel  of  Fig.  28  restored 
by  Correct  Heat-treatment 


?.& 


Fig.  30.     Burnt  Steel  showing 
Cracks  between  Crystals 


Fig.  31.     Casehardened  Steel  showing         Fig.  32.     Crack  between  Carburized 
Unequal  Carburization  Shell  and  Core 


io8  IRON  AND   STEEL 

Fig.  15  shows  the  appearance  of  a  crucible  steel  of  comparatively 
high  carbon  content  in  its  annealed  and  unworked  condition. 
Figs.  1 6  and  17  show  the  same  steel  subjected  to  different  kinds 
of  mechanical  treatment,  and  Figs.  18  to  21,  the  same  steel 
heated  and  quenched  at  different  temperatures.  The  change  in 
structure;  when  the  steel  is  heated  above  its  correct  hardening 
temperature,  is  very  evident.  Figs.  22  and  23  show  the  marten- 
site  structure  of  steel  in  a  very  satisfactory  manner,  while  Figs. 
24  to  26  show  the  structure  in  hardened  steel  drawn  to  different 
temperatures.  Fig.  28  shows  very  clearly  the  coarse-grained 
crystalline  structure  of  overheated  steel,  and  Fig.  29  the  same 
steel  restored  as  nearly  as  possible  to  its  finer  grain  by  correct 
heat-treatment.  Fig.  30  shows  a  burnt  steel  with  cracks  between 
the  crystals,  and  Figs.  31  and  32,  casehardened  steel  unevenly 
carburized  and  with  a  crack  between  the  carburized  shell  and 
core. 

Etching  Reagents  for  Hardened  Steel.  —  The  etching  re- 
agents that  can  be  used  on  annealed  steel  are  not  suitable  for 
hardened  steel.  For  the  latter,  good  results  are  obtained  by  a 
solution  composed  of  4  parts  of  sulphur  dioxide  in  96  parts  of 
water.  The  specimens  are  immersed  in  this  with  the  face  up- 
ward, and  removed  when  the  polished  surface  appears  to  be 
frosted,  the  time  required  being  anywhere  from  a  few  seconds  to 
one  minute.  They  are  then  rinsed  in  water  and  dried  in  alcohol. 
This  etching  reagent  gives  different  colors  to  the  different  con- 
stituents. Austenite  is  pale  brown;  martensite,  from  pale  blue 
to  brown;  troostite,  very  dark;  sorbite,  uncolored;  cementite, 
brilliant  white;  and  ferrite,  a  dark  brown.  Various  other 
etching  reagents  can  also  be  used  to  give  different  colors  to  the 
various  constituents. 

Permeameter  for  Magnetic-mechanical  Analysis.  —  Research 
work  done  abroad  and  at  the  U.  S.  Bureau  of  Standards  has 
shown  that  the  magnetic  properties  of  iron  and  steel  afford  a 
most  valuable  index  to  the  structural  conditions  existing  in 
such  materials,  which  is  of  special  importance  in  those  materials 
intended  for  use  where  strength  or  cutting  properties  are  the 
essential  factors.  Not  only  do  the  initial  processes  of  manufac- 


CHARACTERISTICS  OF  STEEL  109 

ture  affect  the  magnetic  characteristics,  but  subsequent  heat- 
treatment  also;  therefore,  the  magnetic  test  offers  means  of 
examining  materials,  tools,  etc.,  during  and  after  manufacture, 
without  injuring  or  marring  them,  with  a  view  to  predetermin- 
ing their  mechanical  performance. 

The  method  of  "  magnetic-mechanical  analysis"  is  based  upon 
the  fundamental  fact  that  there  is  only  one  set  of  mechanical 
characteristics  corresponding  to  a  given  set  of  magnetic  charac- 
teristics, and  conversely  there  is  only  one  set  of  magnetic  char- 
acteristics corresponding  to  a  given  set  of  mechanical  char- 
acteristics. The  International  Association  for  Testing  Materials, 
The  American  Society  for  Testing  Materials,  the  U.  S.  Bureau 
of  Standards,  and  a  number  of  private  investigators  are  ac- 
tively engaged  on  this  important  work,  so  that  the  science  of 
properly  correlating  the  underlying  factors  will  surely  make 
rapid  progress  in  the  near  future,  especially  since  accurate  and 
convenient  apparatus  has  now  been  developed  to  permit  the 
practical  application  of  this  method  of  analysis  in  the  industries. 
There  are  many  advantages  of  "magnetic-mechanical  analysis" 
which  are  of  great  importance.  The  material  actually  entering 
into  the  construction  of  the  finished  product  and,  in  most  cases, 
the  final  product  itself  can  be  subjected  to  the  test  without 
suffering  the  slightest  injury.  The  various  methods  of  testing 
now  largely  used  (chemical,  microscopic,  hardness,  tensile,  im- 
pact, etc.)  are  either  destructive  or  local  surface  tests.  A 
wholly  different  line  of  testing  from  that  now  employed  is  opened 
by  these  magnetic  investigations;  that  is,  the  reaction  of  the 
material  to  forms  of  energy  which  have  no  permanent  effect  on 
the  material  itself.  Besides  the  point  of  destruction,  the  im- 
portant question  of  "sampling  error"  enters  into  all  the  old 
methods  of  chemical  and  physical  tests. 

Another  important  feature  of  the  magnetic-mechanical  test 
is  that  it  shows  quite  clearly  differences  in  the  mechanical 
properties  of  steel,  where  the  other  methods  of  test  fail  to  in- 
dicate them,  and  where  practice  has  shown  that  such  differences 
do  exist.  Two  pieces  of  steel  may  have  the  same  Brinell  hard- 
ness, for  instance,  and  still  possess  entirely  different  mechanical 


HO  IRON  AND  STEEL 

characteristics.  The  magnetic-mechanical  test  is  not  restricted 
to  work  in  the  laboratory.  Products  like  tools,  saw  blades, 
drills,  ball  bearing  races,  milling  cutters,  etc.,  can  be  subjected 
to  routine  tests  in  the  plant,  and  in  case  some  of  these  show  dis- 
tinct differences  in  magnetic  properties  against  the  average  run, 
it  is  safe  to  assume  that  something  is  wrong  with  their  mechanical 
properties,  so  that  "seconds"  can  be  easily  separated  and  the 
quality  of  tools  of  established  trademark  can  be  at  all  times 
fully  maintained.  Among  the  many  other  steel  products  which 
readily  lend  themselves  to  this  method  of  test  are  files,  knives, 
drill  rods,  wires  and  wire  ropes,  springs,  steel  balls,  plates,  sheets, 
strips,  etc.  Fig.  33  shows  a  typical  Fahy  permeameter  for 
magnetic-mechanical  analysis  of  wires,  wire  ropes,  and  rods, 
and  this  apparatus  is  of  considerable  importance  at  this  time  for 
testing  the  wires  used  in  airplane  construction.  Not  a  "  speci- 
men" of  the  material  is  subjected  to  the  test,  but  the  wires  and 
cables  actually  entering  into  the  construction  of  the  planes. 
The  slightest  lack  of  homogeneity  or  otherwise  invisible  defects 
in  the  stranded  wires  are  clearly  shown  up  and  danger  is  thus 
prevented.  Similar  tests  can  be  applied  to  elevator  and  hoisting 
cables;  in  such  cases  the  apparatus  is  mounted  permanently  and 
defects  can  be  detected  before  accidents  happen.  The  main 
reason  why  this  important  method  has  not  found  considerably 
wider  practical  application  heretofore  was  the  difficulty  in  the 
operation  of  the  instruments  which  had  been  available  for  con- 
ducting magnetic  tests. 

Effect  of  Different  Elements  on  Steel.  —  The  different  ele- 
ments that  enter  into  steel  —  carbon,  manganese,  phosphorus, 
sulphur,  and  silicon  —  all  have  a  decided  influence  upon  the 
quality  of  the  steel.  The  methods  used  in  the  production  of 
special  alloy  steels  also  lend  peculiar  characteristics  to  the  steel. 
In  the  following  paragraphs,  the  effects  of  those  elements  that 
may  be  present  in  all  classes  of  steel  will  be  dealt  with,  while  the 
effect  of  nickel,  chromium,  vanadium,  tungsten,  titanium,  etc.,  will 
be  dealt  with  in  subsequent  chapters  covering  alloy  and  tool  steels. 

Effect  of  Carbon  on  Steel.  —  The  general  influence  of  carbon 
on  steel  is  to  increase  the  tenacity,  hardness,  and  stiffness.  The 


CHARACTERISTICS   OF   STEEL 


III 


tensile  strength  is  increased  from  600  to  800  pounds  per  square 
inch  for  each  additional  point  of  carbon,  while  the  ductility  is 
decreased  about  0.5  per  cent  for  each  point.  Steel  having  a 
carbon  content  of  0.20  per  cent  begins  to  show  an  appreciable 
hardening  effect  when  cooled  quickly.  In  the  normal  or  an- 
nealed state,  steel  will  begin  to  show  evidence  of  brittleness  when 
the  carbon  has  reached  approximately  0.70  per  cent. 


Fig.  33.  Apparatus  for  Investigation  of  Mechanical  Properties  of  Iron 
and  Steel  Wires,  Ropes,  Rods,  etc.,  by  Determination  of  their  Cor- 
related Magnetic  Characteristics 

High-grade  razor  steel  contains  about  1.25  per  cent  of  carbon; 
spring  steel,  i  per  cent;  steel  rails,  from  0.50  to  0.75  per  cent; 
and  soft  steel  boiler  plate  may  have  as  little  as  o.io  per  cent  of 
carbon,  or  even  less.  Steel  which  is  very  low  in  carbon  can  easily 
be  welded,  but  it  cannot  be  hardened;  when  the  carbon  content 
is  above  0.33  per  cent,  welding  is  more  difficult  and  can  only  be 
done  by  the  use  of  borax  or  some  other  flux,  or  by  the  electric 
or  thermit  method.  Steel  with  carbon  above  0.75  per  cent  can 


112  IRON  AND   STEEL 

be  hardened,  that  is,  when  heated  to  red  heat  and  then  quenched 
in  water  or  other  liquid,  it  becomes  very  hard  and  can  be  used  for 
tools  of  various  kinds,  such  as  saws,  files,  drills,  chisels,  cutlery, 
etc.  The  manufacture  of  steel,  therefore,  depends  principally 
upon  obtaining  the  right  proportion  of  carbon. 

Effect  of  Manganese  on  Steel.  —  Manganese  increases  the 
tensile  strength  of  steel  by  about  100  pounds  per  square  inch  for 
each  additional  point,  while  the  ductility  is  probably  somewhat 
decreased,  but  this  effect  is  not  so  marked.  For  medium  steel, 
the  manganese  content  is  usually  from  0.40  to  0.60  per  cent. 
More  or  less  manganese  may  be  specified  for  special  purposes, 
depending  upon  the  amount  of  other  impurities,  although  for 
steel  to  be  heat-treated,  especially  in  the  presence  of  high  carbon, 
high  manganese  is  objectionable.  Steel  with  more  than  i  per 
cent  of  manganese  should  be  avoided,  because  of  its  increased 
hardness  and  tendency  to  brittleness,  except  when  manganese 
enters  into  special  steel  as  an  alloying  element;  in  the  so-called 
" manganese  steel"  the  manganese  varies  from  7  to  12  per  cent. 

Effect  of  Phosphorus  on  Steel.  —  Phosphorus  increases  the 
strength  of  steel,  but  owing  to  its  tendency  to  render  the  metal 
cold-short,  or  brittle,  it  should  be  considered  as  an  impurity 
and  avoided  as  much  as  possible.  The  lower  the  phosphorus 
content  the  better,  except  possibly  in  spring  steel,  where  a  min- 
imum limit  is  frequently  specified. 

The  specifications  for  steel  intended  for  constructional  pur- 
poses usually  limit  the  phosphorus  content  to  from  0.04  to  0.08 
per  cent,  depending  upon  the  class  of  steel  and  the  process  of 
manufacture.  (See  specifications  under  following  paragraph 
on  " Effect  of  Sulphur  on  Steel.")  When  a  structure  is  sub- 
jected to  static  loading  only,  Bessemer  steel  may  be  acceptable 
with  the  phosphorus  content  limited  to  0.08  per  cent.  Accord- 
ing to  some  authorities,  a  higher  phosphorus  content  than  is 
commonly  specified  will  not  cause  the  injurious  effects  frequently 
attributed  to  this  element.  According  to  a  paper  presented 
before  the  Iron  and  Steel  Institute  in  London,  by  Dr.  J.  E. 
Stead,  on  the  "  Influence  of  Some  Elements  on  the  Mechanical 
Properties  of  Steel,"  there  is  no  reliable  record  showing  that 


CHARACTERISTICS  OF  STEEL  113 

sound  steel  rails  containing  from  0.07  to  0.09  per  cent  of  phos- 
phorus break  on  the  track  more  frequently  than  those  containing 
less  phosphorus.  It  is  also  claimed  that  phosphoretic  rails  resist 
wear  better  than  the  same  rails  having  less  of  this  element;  in 
fact,  when  iron  rails  were  in  use,  it  was  the  practice  to  have  the 
iron  very  rich  in  phosphorus  in  the  heads  of  the  rails  in  order  to 
make  them  wear  better.  When  steel  was  introduced,  carbon 
replaced  phosphorus. 

Phosphorus  tends  to  give  steel  clean  bright  surfaces  and  in- 
creases the  elastic  limit  and  tenacity.  From  0.13  to  0.20  per 
cent  is  required  to  give  steel  good  machining  properties.  When 
phosphorus  is  alloyed  with  iron,  the  metal  is  less  liable  to  corrode 
and  it  is  useful  in  this  respect.  Phosphorus  is  also  introduced 
into  tin-plate  bars,  as  it  prevents  the  sheets  from  sticking  to- 
gether during  rolling.  Phosphorus,  therefore,  is  not  invariably 
an  injurious  element,  although  the  use  of  high  phosphorus  steels 
in  general  is  not  advocated. 

Effect  of  Sulphur  on  Steel.  —  Sulphur  is  generally  classified 
as  an  injurious  element  in  steel,  although  recent  experiments  and 
tests  indicate  that  the  effect  of  sulphur  has  not  been  fully  un- 
derstood and  that  many  specifications  require  much  smaller 
amounts  of  both  phosphorus  and  sulphur  than  is  necessary. 
In  the  paper  by  Dr.  J.  E.  Stead,  previously  referred  to,  a  number 
of  important  points  regarding  the  influence  of  sulphur  were 
mentioned.  To  begin  with,  the  effect  of  sulphur  alone  on  steel 
without  manganese  is  to  produce  red  shortness,  and  injurious 
effects  attributed  to  sulphur  in  the  early  days  of  steel-making 
were  doubtless  due  to  the  difficulty  of  getting  a  sufficient  quan- 
tity of  manganese  into  the  steel  without  unduly  increasing  the 
carbon  content,  because  at  that  time  the  only  spiegeleisen  avail- 
able contained  about  4.5  per  cent  of  carbon  and  from  7  to  9  per 
cent  of  manganese.  When  spiegeleisen  was  produced  containing 
20  per  cent  of  manganese,  there  was  little  or  no  red  shortness, 
and  when  the  manganese  was  still  further  increased,  sulphur 
ceased  to  be  the  injurious  element  it  had  been  previously. 

Manganese  counteracts  the  effect  of  sulphur,  but  steel  rails 
and  other  parts  of  exceptional  quality  are  ofteii  rejected  because 


114  IRON  AND   STEEL 

the  sulphur  content  exceeds  arbitrary  limits  even  when  all 
mechanical  tests  have  proved  that  the  material  is  satisfactory. 
In  an  exhaustive  series  of  tests,  steel  containing  0.15  per  cent  of 
sulphur  gave  better  impact  tests  than  any  of  the  other  steels 
used,  and  it  proved  much  superior  to  a  similar  steel  containing 
only  0.015  per  cent  of  sulphur.  Sulphurous  steel,  however,  is 
weaker  when  tested  transversely.  For  example,  ship  and  boiler 
plates  high  in  sulphur  are  weaker  transversely  than  in  the  direc- 
tion in  which  they  were  most  extended  by  rolling.  When  the 
steel  is  to  be  stressed  transversely  to  the  rolling  direction,  the 
sulphur  should  be  low,  but  if  it  is  stressed  in  line  with  the  rolling 
direction,  sulphur  is  not  considered  detrimental.  Steel  high  in 
sulphur  resembles  wrought  iron  and  is  more  or  less  fibrous.  In 
fact,  sulphur  is  deliberately  introduced  into  a  class  of  steel  known 
as  "  free-cutting  fibrous  steel"  which  contains  about  0.15  per 
cent  of  sulphur.  A  moderate  amount  of  sulphur  tends  to  pro- 
duce smooth  machine  surfaces  as  compared  with  a  low  sulphur 
steel  which  is  relatively  difficult  to  machine. 

While  some  of  the  preceding  references  to  sulphur  might  be 
regarded  as  favorable  to  a  relatively  high  sulphur  content,  the 
author  of  the  paper  previously  mentioned  emphasizes  the  fact 
that,  in  general,  the  less  sulphur  and  phosphorus,  the  better. 
The  point  is  that  for  certain  purposes  these  elements  may  confer 
desirable  properties  upon  steel.  The  more  sulphur  steel  con- 
tains, other  conditions  being  constant,  the  more  rapidly  it  is 
attacked  by  acid  solvents.  It  has  also  been  alleged  that  high 
sulphur  is  conducive  to  increased  corrosion.  Sulphur  has  a 
tendency  to  render  steel  red  short,  so  that  it  is  to  be  avoided  in 
any  steel  that  must  be  forged  or  otherwise  worked  hot.  Hot 
shortness  is  also  liable  to  cause  trouble,  especially  in  steel  that  is 
to  be  casehardened  or  heat-treated. 

The  Manufacturers  Standards  Specifications  for  structural 
steel,  as  revised  April,  1914,  includes  three  classes  of  structural 
steels  designated  as  Class  A,  which  is  used  for  railway  bridges 
and  ships;  Class  B,  for  buildings,  highway  bridges,  and  similar 
structures;  and  Class  C,  for  structural  rivets.  Classes  A  and  C 
must  be  made  by  the  open-hearth  process,  whereas  Class  B 


CHARACTERISTICS  OF  STEEL  115 

may  be  made  either  by  the  open-hearth  or  Bessemer  process. 

Class  A:  —  The  maximum  phosphorus  content,  when  made  by 
the  basic  open-hearth  process,  is  0.04  per  cent;  when  made  by 
the  acid  open-hearth  process,  0.06  per  cent.  The  maximum  sul- 
phur content  is  0.05  per  cent. 

Class  B :  —  The  maximum  phosphorus  content,  when  made  by 
the  basic  open-hearth  process,  is  0.06  per  cent;  when  made  by 
the  acid  open-hearth  process,  0.08  per  cent;  and  when  made 
by  the  Bessemer  process,  o.io  per  cent.  The  sulphur  content  is 
not  specified. 

Class  C :  —  The  maximum  phosphorus  content,  when  made  by 
either  the  acid  or  the  basic  open-hearth  process,  is  0.04  per  cent. 
The  maximum  sulphur  content  is  0.045  Per  cent. 

Effect  of  Silicon  on  Steel.  —  Silicon  is  generally  supposed  to 
render  steel  cold-short,  but  there  is  little  evidence  that  silicon 
in  a  small  quantity  will  do  this.  In  ordinary  steel,  the  silicon 
is  usually  limited  to  0.20  per  cent,  but  there  are  special  silicon 
steels  where  the  silicon  tends  to  increase  the  tensile  strength  but 
decreases  the  elongation  and  reduction  of  area. 

Effect  of  Copper  on  Steel.  —  It  has  been  found  that  steel 
containing  from  0.30  to  0.35  per  cent  of  carbon,  from  0.25  to 
0.35  per  cent  of  silicon,  from  i.oo  to  1.20  per  cent  of  manganese, 
from  1.50  to  i. 80  per  cent  of  nickel,  from  0.50  to  0.80  per  cent  of 
copper,  and  not  over  0.05  per  cent  of  phosphorus  and  sulphur  will 
have  the  same  properties  as  a  3-per-cent  nickel  steel.  When 
properly  heat-treated,  it  will  have  a  tensile  strength  of  95,000 
pounds  per  square  inch,  an  elastic  limit  of  65,000  pounds,  an 
elongation  of  18  per  cent,  and  a  reduction  of  area  of  30  per  cent. 
If  the  steel  also  contains  0.50  per  cent  of  chromium,  its  physical 
properties  will  be  the  same  as  a  steel  containing  i  per  cent  of 
chromium  and  3  per  cent  of  nickel.  Its  tensile  strength  will 
then  be  140,000  pounds  per  square  inch;  its  elastic  limit,  110,000 
pounds  per  square  inch;  its  elongation,  17  per  cent;  and  its 
reduction  of  area,  44  per  cent.  The  addition  of  copper  dimin- 
ishes the  brittleness  of  the  steel  at  low  temperatures. 

Influence  of  Various  Metals  on  Corrosiveness  of  Steel.  - 
Silicon  in  steel  increases  greatly  its  tendency  to  corrode;  0.3 


Il6  IRON  AND   STEEL 

per  cent  of  silicon  will  make  iron  rust  20  per  cent  more  rapidly 
than  would  ordinary  steel  free  from  silicon.  On  the  other  hand, 
alloying  steel  with  nickel  or  copper  gives  it  increased  resistance 
to  corrosion;  0.2  per  cent  of  copper  in  steel  produces  a  material 
which  is  attacked  by  acids  at  one-tenth  the  rate  of  ordinary  steel. 
The  corrosion  in  the  atmosphere  is  only  one-third  that  of  steel 
free  from  copper.  An  increase  of  copper  above  0.2  per  cent  does 
not  add  to  the  corrosion-resisting  qualities  of  the  steel.  These 
results  have  been  obtained  not  merely  by  laboratory  experiments 
but  in  practice.  Roofs  have  been  covered  in  and  around  Pitts- 
burg  with  ordinary  sheet  steel  and  also  with  a  sheet  steel  con- 
taining 0.2  per  cent  of  copper.  The  copper-alloy  roofs  were  in 
good  condition  when  the  ordinary  sheet-iron  roofs  were  com- 
pletely corroded. 

Necessity  of  Various  Elements  in  Steel.  —  Carbon  and  man- 
ganese add  most  to  the  strength  of  steel  in  proportion  to  what 
they  detract  from  the  ductility,  and  are,  therefore,  the  most 
desirable  elements  to  have  present.  It  is,  however,  neither 
desirable  nor  possible  to  have  a  steel  free  from  all  elements  but 
these.  The  other  elements  are  present  as  impurities  in  the  iron 
ore  and  the  fuel,  and  while  it  is  generally  possible  to  reduce  them 
to  a  very  small  amount,  it  is  impossible  to  eliminate  them  en- 
tirely. Then,  too,  the  presence  of  some  of  these  impurities  is 
absolutely  necessary  in  order  that  the  steel  shall  be  sound  and 
readily  worked.  Silicon,  in  particular,  has  a  highly  beneficial 
effect  in  making  the  steel  more  sound  and  homogeneous. 

Steel  having  a  very  small  percentage  of  impurities  has  two 
faults:  i.  When  the  liquid  mass  is  cast  into  an  ingot,  the  im- 
purities tend  to  gather  into  one  place,  thus  forming  hard  brittle 
spots  in  a  steel  that  is  otherwise  too  soft  and  weak.  This 
trouble  is  termed  "  segregation,"  and  is  obviated  by  a  sufficient 
proportion  of  impurities,  the  most  efficient  in  overcoming  it  being 
silicon.  2.  Gas  is  present  in  the  cooling  mass  in  the  form  of 
bubbles,  which  form  vacant  spaces  in  the  ingot  and  when  flat- 
tened out,  in  working,  become  flaws  in  the  finished  piece.  The 
remedy  for  this  fault,  also,  is  a  larger  proportion  of  impurities, 
and  especially  silicon. 


CHAPTER  VI 
CRUCIBLE   STEEL 

THE  crucible  process  was  formerly  used  for  making  all  the 
high-grade  tool  steel  used  for  metal-cutting  tools  and,  conse- 
quently, the  terms  "  tool  steel"  and  "  crucible  steel"  are  often 
used  interchangeably,  but  at  the  present  time  the  electric  fur- 
nace is  used  extensively  for  producing  tool  steel  which  should 
not  be  classified  as  crucible  steel.  Few  mechanical  processes 
have,  during  the  general  progress  of  engineering,  undergone  so 
little  change  as  the  methods  employed  in  the  making  of  tool 
steel  by  the  crucible  process.  With  the  exception  of  a  more 
direct  method  for  introducing  the  carbon  into  the  steel,  it  may 
be  said  that,  in  general,  the  same  methods  are  still  used  as  were 
employed  a  century  ago,  although  improved  methods  for  heat- 
ing the  furnaces  and  for  handling  and  working  the  steel  at  the 
various  stages  of  manufacture  have  been  introduced  during 
the  course  of  mechanical  development.  Briefly  described,  the 
method  of  producing  crucible  or  tool  steel  consists  in  using 
wrought  iron  containing  as  small  a  percentage  of  phosphorus  and 
sulphur  as  possible,  and  adding  carbon  to  it.  Two  methods 
have  been  in  use  for  accomplishing  this  result,  the  older  one  being 
the  so-called  "  cementation"  process,  the  newer  being  the  regular 
crucible  process. 

Cementation  Process.  —  The  cementation  process  is  similar, 
in  principle,  to  the  ordinary  casehardening  process  for  giving 
parts  made  of  low-carbon  machine  steel  a  hard  high-carbon  sur- 
face. In  the  cementation  process,  wrought-iron  bars  are  packed 
in  long  air-tight  cast-iron  retorts  containing  enough  pulverized 
charcoal  so  that  each  bar  will  be  well  bedded  in  it.  When  the 
retorts  are  thus  filled,  they  are  placed  in  a  furnace,  called  the 
"cementation  furnace,"  where  they  are  heated  to  a  red  heat, 
at  which  temperature  they  are  kept  for  several  days  —  anywhere 

.117 


Il8  IRON  AND   STEEL 

from  six  to  ten  days  —  after  which  they  are  permitted  to  cool 
down  slowly.  When  the  bars  are  heated,  they  absorb  carbon 
from  the  charcoal  in  which  they  are  packed.  The  amount  ab- 
sorbed depends  upon  the  length  of  time  they  are  exposed  to  the 
high  temperature.  The  absorption  of  carbon  may  amount  to  as 
much  as  ij  per  cent.  The  product  obtained  by  this  process  is 
known  as  "  blister  steel, "  as  the  surface  of  the  bars  is  covered 
with  small  scales  or  blisters.  When  cool,  the  blister  bars  are 
hammered  into  longer  bars,  which  are  then  cut,  piled,  heated, 
welded,  and  again  hammered  out  into  bars.  The  product  so 
obtained  is  known  as  "  single  shear  steel."  When  this  is  again 
cut,  piled,  heated,  welded,  and  hammered  out  into  bars,  the 
product  is  known  as  "double  shear  steel."  This  method  of 
producing  tool  steel  does  not  render  as  uniform  a  material  as  the 
regular  crucible  process,  as  the  amount  of  carbon  in  the  bar 
varies;  it  is  greatest  at  the  surface  and  least  near  the  center. 

Crucible  Process.  —  In  order  to  obtain  a  more  uniform  steel 
than  that  produced  by  the  cementation  process,  Benjamin 
Huntsman,  a  Sheffield  watchmaker,  about  1740,  devised  a 
process  of  melting  blister  bars  in  clay  pots  or  crucibles.  This 
method  is  still  used  for  the  production  of  some  Sheffield  tool  steel; 
blister  bars  made  from  Swedish  charcoal  iron  of  uniform  carbon 
content  being  used  for  the  raw  material.  The  American  method 
of  producing  crucible  steel  is  similar  to  this,  except  that,  instead 
of  using  blister  bars,  wrought  iron  is  melted  directly  in  crucibles 
without  any  cementation  process  preceding  this  melting/  and  the 
carbon  is  added  directly  in  the  crucible  in  the  form  of  powdered 
charcoal.  The  wrought  iron  is  cut  up  into  small  pieces  before 
being  put  into  the  crucible.  The  charge  is  melted  and  is  per- 
mitted to  remain  in  the  molten  state  for  some  time  before  being 
poured  into  molds.  While  in  the  molten  state,  the  iron  absorbs 
carbon  much  more  quickly  than  when  only  red  hot,  as  in  the 
cementation  process.  When  the  carbon  is  added  directly  in 
the  crucible,  it  is  also  possible  to  more  accurately  determine  the 
carbon  content  of  the  final  product,  and,  for  this  reason,  the 
crucible  process,  as  employed  in  America,  is  held  to  be  superior 
to  the  crucible  process  using  blaster  steel.  Steel  containing  the 


CRUCIBLE  STEEL 

required  amount  of  carbon  is  obtained  in  a  few  hours,  while,  by 
the  original  Huntsman  process,  a  period  of  nearly  two  weeks  is 
required. 

There  are  some  variations  in  the  raw  material  used  for  crucible 
steel.  In  Sweden,  wrought  iron  and  pig  iron  are  sometimes 
melted  together,  and  also  pig  iron  and  iron  ore,  but  these  methods 
have  not  been  used  to  any  extent  in  the  United  States.  American 
makers,  however,  have  used  Bessemer  and  open-hearth  soft  steel 
instead  of  wrought  iron,  for  a  number  of  years,  but  this  process 
gives  an  inferior  product.  The  best  material  for  the  making  of 
crucible  steel  is  generally  conceded  to  be  Swedish  (Dannemora) 
wrought  iron  having  a  carbon  content  of  from  o.io  to  0.20  per 
cent.  This  iron  comes  in  flat  bars,  i  by  2  inches,  and  is  cut  up 
into  small  pieces  about  i  inch  wide.  Swedish  wrought  iron  is 
used  in  preference  to  the  domestic  material,  because  it  produces 
a  superior  tool  steel.  It  is  possible  to  obtain  domestic  wrought 
iron  having  by  chemical  analysis  practically  the  same  composition 
as  the  Dannemora  iron,  but  the  tool  steel  made  from  it  will  not 
be  of  as  good  a  quality.  Some  metallurgists  claim  that  the 
reason  for  this  is  that  the  Swedish  iron  ore  originally  contains  a 
small  amount  of  vanadium,  which,  while  it  is  eliminated  during 
the  process  through  which  wrought  iron  is  produced,  so  that  it  is 
not  present  in  the  wrought  iron  itself,  nevertheless  has  an  in- 
fluence upon  the  quantity  of  wrought  iron,  because  of  its  effect 
in  making  the  iron. 

The  reasons  generally  given  for  the  superiority  of  crucible 
steel  are  that  a  metal  almost  free  from  sulphur  and  phosphorus  is 
used  as  the  raw  material;  the  iron,  when  in  the  molten  condition, 
is  protected  from  the  oxidizing  gases  of  the  furnace  by  being 
kept  in  a  covered  crucible;  and  the  carbon  content  can  be  very 
accurately  controlled. 

Crucibles  Used.  —  The  crucibles  used  in  the  crucible  process 
for  making  tool  steel  are  either  made  from  clay  or  graphite,  and 
hold  anywhere  from  60  to  125  pounds.  Generally,  the  height 
of  the  crucible  is  about  20  inches,  and  its  diameter,  about  12 
inches  at  the  central  or  largest  part.  When  placed  in  the  fur- 
nace, the  crucible  is  provided  with  a  fireclay  cover.  A  crucible 


120  IRON  AND   STEEL 

of  the  dimensions  mentioned  will  have  a  capacity  of  from  75  to 
80  pounds  of  iron. 

Clay  Crucibles.  —  Clay  crucibles  are  generally  used  in  Europe, 
while  graphite  crucibles  are  preferred  by  many  steel-makers  in 
America;  while  their  first  cost  is  greater  than  that  of  clay  cru- 
cibles, they  are  stronger  and  last  longer.  There  are,  however, 
several  American  steel-makers  who  prefer  clay  crucibles,  es- 
pecially in  the  making  of  high-grade  tool  steel,  because,  when  a 
clay  crucible  is  used,  there  is  no  possibility  for  any  extraneous 
matter  mixing  with  the  charge,  and  the  carbon  content  can  be 
very  closely  predetermined.  When  a  graphite  crucible  is  used, 
small  particles  of  graphite  will  flake  off  on  the  inside  of  the  cru- 
cible, and  these  particles  will  mix  with  the  charge.  It  is  claimed 
that  they  will  not,  however,  enter  into  a  chemical  composition 
with  the  steel,  but  will  merely  mix  with  it  mechanically,  so  that 
there  will  be  small  particles  of  graphite  imbedded  in  the  steel, 
thus  producing  small  holes  and  flaws  in  the  finished  material. 
The  only  disadvantage  of  the  clay  crucible  is  that  it  is  easily 
broken  when  cold,  and  is  also  more  likely  to  break  in  the  furnace, 
nor  will  it  last  as  long  as  graphite  crucibles.  The  latter,  there- 
fore, are  considered  cheaper  in  the  long  run. 

Making  Clay  Crucibles.  —  Clay  crucibles  are  made  from  a 
mixture  of  several  kinds  of  clay.  The  best  quality,  previous  to 
the  war,  was  made  by  mixtures  of  imported  and  domestic  clays, 
in  certain  proportions.  The  essential  qualities  of  the  mixture 
are  that  it,  must  be  strong,  plastic,  and  refractory,  and  that  it 
should  not  contain  any  oxide  of  iron,  alkalies,  or  alkaline  earths. 
In  making  clay  crucibles,  a  form  is  used  to  give  it  the  outside 
shape,  and  a  revolving  former  is  employed  to  shape  the  inside. 
When  the  crucible  has  thus  been  formed,  it  is  permitted  to  dry 
at  ordinary  room  temperature,  after  which  it  is  put  in  an  anneal- 
ing furnace,  where  it  is  slowly  heated  to  a  high  temperature. 
Clay  crucibles  must  be  taken  directly  from  the  annealing  fur- 
nace while  hot,  charged  with  iron  and  charcoal,  and  put  into  the 
melting  furnace,  after  which  the  crucible  must  not  be  allowed 
to  cool  off  until  its  usefulness  is  past.  The  heat  of  the  crucible 
and  charge  while  in  the  furnace  is  from  2500  to  2800  degrees  F. 


CRUCIBLE  STEEL  1 21 

Graphite  Crucibles.  —  Graphite  crucibles  are  made  from  a 
mixture  containing  nearly  equal  amounts  of  graphite  and  clay, 
and  a  small  amount  of  sand.  The  graphite  must  be  well  ground 
or  the  crucible  may  become  porous;  still,  if  ground  too  fine,  the 
walls  of  the  crucible  will  be  so  dense  that  the  conduction  of  heat 
through  them  will  be  slow;  besides  they  will  not  expand  or  con- 
tract quickly  and,  therefore,  will  have  a  tendency  to  crack. 
The  sand  used  is  an  ordinary  fire  or  silica  sand  that  contains 
from  95  to  99  per  cent  of  silica  with  small  amounts  of  alumina, 
alkaline  earths,  or  combined  water.  Oxide  of  iron  and  alkalies 
lower  the  fusion  point,  if  present  except  in  very  small  amounts. 

After  the  ingredients  are  mixed  into  a  thoroughly  homogeneous 
mass,  the  mixture  is  ready  for  molding;  at  this  time  it  contains 
about  22  per  cent  of  water.  Molding  was  formerly  done  by 
hand,  but  now  it  is  done  almost  entirely  by  machines.  In  hand 
molding,  a  form  is  used  to  give  the  outside  shape,  and  a  revolving 
former  is  used  to  shape  the  inside.  The  crucibles  are  first  dried 
at  ordinary  room  temperature,  and  are  then  placed  in  the  an- 
nealing furnace  where  they  are  slowly  heated  to  a  temperature 
of  from  1400  to  1500  degrees  F.;  this  annealing  is  done  in  some 
type  of  pottery  kiln.  If  coal  is  used  as  a  fuel,  the  sulphur  con- 
tent must  be  low,  or  the  crucible  will  be  injured  by  absorbing  too 
much  of  the  sulphur.  When  made,  graphite  crucibles  should  be 
stored  in  a  dry  and,  if  possible,  warm  place,  and  should  be  dried 
out  on  a  furnace  top  for  a  week  or  two  before  being  used.  New 
pots  should  be  heated  by  being  placed  around  the  melting  holes 
before  they  are  charged.  Clay  pots  must  not  be  allowed  to  cool 
off  at  any  time. 

Charging  the  Crucibles.  —  In  England,  the  clay  crucibles  are 
placed  in  the  furnace  and  then  charged,  a  sheet-iron  funnel 
being  used  for  this  work.  The  American  practice,  when  these 
crucibles  are  used,  is  to  heat  the  crucibles  in  the  furnace,  remove 
them  for  the  charging,  and  quickly  replace  them  in  the  furnace. 
Graphite  crucibles  are  charged  when  cold,  after  they  have  been 
tested  for  thickness  and  cracks.  In  some  mills,  the  larger  pieces 
of  iron  and  the  charcoal  are  placed  at  the  bottom  and  the  smaller 
and  more  closely  fitting  pieces  are  placed  at  the  top.  In  other 

8F 


122 


IRON  AND   STEEL 


mills,  one-half  of  the  charge  is  placed  in  the  crucible,  then  a  bag 
containing  the  charcoal,  then  the  rest  of  the  iron.  Fig.  i  shows 
crucible,  a  charge  of  Swedish  iron,  and  a  bag  of  charcoal.  The 
crucible  containing  the  charge  is  covered  with  a  clay  top  and  put 
into  the  furnace.  When  high-speed  steel  is  made,  other  ingredi- 
ents, such  as  chromium,  tungsten,  molybdenum,  etc.,  are  placed 
in  the  crucible  together  with  the  charcoal  and  iron. 

Determination  of  the  Carbon  Content  of  Steel.  —  The  carbon 
content  in  the  steel  is  determined  by  the  amount  of  charcoal  in 
the  charge.  It  is  not  possible,  however,  to  calculate  directly 


Fig.  i.  Charge  for  Making  Crucible  Steel,  consisting  of  Swedish 
Iron,  a  Bag  of  Charcoal,  and  the  Clay  Crucible  in  which  the 
Charge  is  melted 

the  proportions  of  charcoal  necessary  for  a  certain  weight  of  iron 
to  produce  a  given  percentage,  as  some  carbon  is  contained  in  the 
wrought  iron.  Some  of  the  charcoal  is  also  lost  in  the  slag. 
The  common  method  of  determining  the  amount  of  charcoal  re- 
quired is  to  consider  that  each  ounce  of  charcoal  will  give  about 
0.07  per  cent  of  carbon  to  the  steel  in  a  charge  weighing  from 
80  to  90  pounds,  or  "one  ounce  gives  seven  points  of  carbon." 
This  proportion  is  approximately  correct  for  ordinary  carbon 
contents,  but,  when  steel  of  a  very  high  carbon  content  is  re- 
quired, it  is  necessary  to  add  charcoal  in  a  greater  proportion, 


CRUCIBLE  STEEL  123 

partly  because  the  original  amount  of  carbon  in  the  wrought  iron 
is  of  relatively  less  importance,  and  partly  because  more  of  the 
carbon  is  lost  or  wasted. 

Melting  Furnaces.  —  Crucible  furnaces  may  be  heated  by 
coal  or  coke,  oil  or  gas.  When  solid  fuel  is  used,  the  crucibles 
are  practically  buried  in  the  fuel  beds,  but  when  liquid  or  gaseous 
fuels  are  used,  the  crucibles  are  arranged  so  that  the  burning 
gases  pass  around  them. 

A  coal  hole  is  the  name  of  a  furnace  that  burns  a  solid 
fuel.  This  furnace  is  formed  by  making,  in  a  pit  in  the  work- 
room floor,  a  combustion  chamber  which  is  connected  to  the 
chimney  by  a  flue  and  has  a  working  space  in  front  of  it  for  the 
men  attending  to  the  fires.  The  top  of  this  working  space  is 
covered  by  bars  which  admit  light  and  air,  and  also  allow  any 
steel  that  may  be  spilled  during  pouring  to  fall  into  the  pit, 
instead  of  running  over  the  floor.  The  top  of  the  combustion 
chamber  is  protected  by  a  cover.  These  pits  are  generally  lined 
up  along  one  side  of  the  room.  The  melting  hole  is  large  enough 
to  hold  from  four  to  six  crucibles,  and  is  about  four  feet  deep. 
The  forced  blast  is  introduced  into  the  ash-pit,  and  a  short  flue 
connects  the  melting  hole  with  the  main  flue.  The  melting  hole 
cover  is  generally  in  three  sections  to  facilitate  handling. 

In  operation,  a  small  fire  is  started  on  the  grate  bars  and  is 
built  up  until  the  bed  of  glowing  coals  is  about  a  foot  thick. 
Then,  from  six  inches  to  a  foot  of  coal  is  dumped  on  the  fire  and 
the  crucibles  placed  upon  it,  after  which  coal  is  carefully  packed 
around  and  on  top  of  the  pots,  and  air  is  admitted  through  a 
pipe.  The  fire  should  be  blown  gently  at  first,  especially  when 
new  crucibles  are  used,  because,  if  the  crucibles  are  heated  too 
rapidly,  they  will  spall  or  crack.  After  about  two  hours,  the 
crucibles  must  be  raised  and  more  fuel  forced  under  and  around 
them  until  the  fuel  bed  is  level  with  the  top  of  the  crucibles, 
when  the  cover  is  placed  on  the  combustion  chamber  and  the 
fire  is  again  forced.  In  from  one  to  three  hours  more,  the  steel  is 
ready  to  pour. 

In  English  mills,  coke  is  generally  used  as  the  fuel,  but  in,  the 
United  States  anthracite  is  used,  although  sometimes  coke  is 


124  IRON  AND   STEEL 

mixed  with  it.  In  the  latter  case,  when  the  crucibles  are  reset 
in  the  fuel,  anthracite  is  used  almost  entirely,  because  coke  burns 
too  rapidly.  When  coke  is  used,  the  crucibles  must  be  raised 
and  the  fuel  bed  fixed  three  or  more  times  during  a  heat. 

The  advantages  of  this  type  of  furnace  are  its  low  first  cost  and 
its  suitability  for  intermittent  operation;  the  chief  disadvantages 
are  the  high  cost  of  the  steel  due  to  the  low  tonnage  produced, 
the  heavy  wear  on  the  crucibles,  the  high  fuel  consumption,  and 
the  high  cost  of  labor. 

Oil-burning  Furnaces.  —  In  localities  where  oil  is  cheap,  oil- 
burning  furnaces  are  sometimes  used.  In  some  of  these  the  oil 
is  burned  in  a  chamber  alongside  of  the  melting  hole,  and  the 
hot  gases  pass  around  the  crucibles  on  their  way  to  the  chimney. 
In  others,  steam  or  air  is  used  to  atomize  the  oil,  which  is  blown 
into  the  melting  chamber;  the  oil  is  ignited  as  soon  as  it  is  vapor- 
ized. While  these  furnaces  cost  more  to  install  than  a  coal  hole, 
they  are  cheaper  to  work,  because  of  the  reduced  labor  cost,  as 
no  coal  or  ashes  need  be  handled.  The  melting  also  is  more 
rapid,  giving  a  larger  output. 

Gas-fired  Regenerative  Furnace.  —  Most  crucible  furnaces 
are  of  the  regenerative  type.  They  are  heated  by  gas  which, 
with  the  air  necessary  for  its  combustion,  passes  into  the  furnace 
alternately  from  either  the  one  side  or  the  other.  When  the  gas 
enters  on  one  side,  the  exhaust  gases  pass  out  through  a  checker- 
brickwork  on  the  other  side.  The  exhaust  gases  being  of  a 
very  high  temperature  heat  this  checker-brickwork  to  a  red  heat. 
At  this  time,  the  entering  gas  is  automatically  shut  off  from  the 
one  side,  and  gas  is  now  admitted  from  the  opposite  side  that 
has  been  heated  by  the  exhaust  gases.  This  gas  then,  passing 
through  the  heated  checker-brickwork,  is  thoroughly  pre- 
heated, so  that  when  combustion  takes  place,  a  much  higher 
degree  of  heat  is  obtained.  The  combustion  gases  from  this 
side  now  heat  the  checker-brickwork  on  the  other  side,  and  the 
process  of  preheating  the  gas  as  it  enters  alternately  from  the 
two  sides  of  the  furnace  is  thus  automatically  taken  care  of. 

As  in  the  other  types,  this  furnace  is  usually  placed  below  the 
working-room  floor,  so  that  the  crucibles  are  easily  handled. 


CRUCIBLE   STEEL 


125 


Air  is  admitted  through  the  outside  chamber  A,  Fig.  2,  and  gas 
through  the  inner  chamber  B.  As  they  mix,  they  ignite  and 
pass  into  the  melting  chamber,  and  then  through  chambers  D 
and  E  to  the  chimney.  When  the  brickwork  in  chambers  D 
and  E  is  heated  to  the  desired  temperature,  the  valves  are 
turned,  and  the  gas  and  air  are  supplied  to  the  furnace  through 
chambers  D  and  E,  while  the  waste  gases  pass  off  through  cham- 
bers A  and  B.  This  reversal  of  the  flow  of  the  gas  and  air  and 
the  waste  gases  is  made  at  regular  intervals.  It  is  immaterial 
whether  the  gas  chambers  are  on  the  inside  of  the  air  chambers, 


•p^£^^ 

'^Machinery 


Fig.  2.     Gas-fired  Regenerative  Crucible  Furnace 

as  here  shown,  or  on  the  outside,  so  long  as  the  air  is  arranged  to 
enter  above  the  gas.  This  furnace  is  the  most  costly  to  install, 
but  is  the  cheapest  to  operate,  and  may  be  used  with  producer  or 
natural  gas.  When  natural  gas  is  used,  only  the  air  is  preheated, 
so  that  both  sets  of  checkerwork  chambers  are  used  for  air  or 
only  one  set  is  provided.  The  bottom  of  the  melting  chamber  is 
generally  provided  with  a  bed  of  coke  breeze,  to  prevent  the  cru- 
cibles from  sticking  to  the  brick  lining  of  the  melting  chamber. 
The  Krupp  regenerative  furnace,  which  is  used  mostly  in  Ger- 
many, is  built  above  the  floor  and  has  a  closed  top.  The  cruci- 
bles are  put  into  and  drawn  from  it  through  openings  in  the  side. 
This  furnace  is  not  extensively  used  in  the  United  States.  One 
objection  to  it  is  that  the  condition  of  the  steel  cannot  be  known 
unless  one  goes  to  the  top  of  the  furnace  and  looks  through  small 


126  IRON  AND  STEEL 

holes  in  the  roof.  Another  objection  is  that  any  steel  that  may 
be  spilled  is  supposed  to  run  to  the  back  of  the  furnace  and  then 
to  flow  out  through  a  tap  hole.  The  gases,  however,  soon  change 
this  iron  into  a  carbonless  iron  that  will  not  run  through  the  tap 
hole  and  which  must  be  pried  off  the  bottom  of  the  hearth,  when 
it  frequently  takes  part  of  the  bottom  of  the  hearth  with  it. 

Operating  the  Crucible  Furnace.  —  The  charging  floor,  or  the 
floor  on  which  the  men  work  who  insert  the  crucibles  in,  and 
remove  them  from,  the  furnace,  is  level  with  the  top  of  the  fur- 
nace in  all  the  ordinary  American  and  British  types.  Firebrick 
covers  are  kept  over  the  openings  of  the  furnace  at  all  times 
except  when  a  crucible  is  being  put  in  place  or  removed.  Re- 
generative furnaces  are  always  kept  running  continuously  day 
and  night,  as  they  would  crack  and  be  destroyed  by  the  severe 
internal  stresses  due  to  sudden  cooling,  if  the  fire  were  permitted 
to  go  out.  The  life  of  a  regenerative  furnace  is  usually  from 
six  months  to  a  year,  after  which  time  it  must  be  rebuilt. 

The  crucibles  are  placed  into,  and  lifted  out  of,  the  furnace 
by  means  of  large  tongs,  the  men  doing  the  work  standing  partly 
over  the  furnace  while  removing  the  crucible.  When  it  is 
thought  that  a  charge  in  the  crucible  is  melted,  which  requires 
anywhere  from  two  to  five  hours,  the  melter  slides  the  lid  from 
each  pot  in  succession,  in  order  to  examine  the  condition  of  the 
steel.  When  first  melted,  the  steel  boils  quite  freely,  but  as  the 
metal  is  held  at  that  temperature  for  some  time,  the  boiling 
gradually  subsides.  This  holding  of  the  metal  at  a  high  tempera- 
ture until  no  more  gas  is  evolved  is  known  as  "  killing"  or  "  dead 
melting,"  and  usually  takes  from  20  minutes  to  an  hour.  In 
order  to  test  the  steel,  the  melter  thrusts  a  light  iron  rod  into  the 
crucible  with  which  he  stirs  the  metal.  If  the  metal  is  "  cold," 
it  is  sluggish  and  pasty,  and  adheres  to  the  rod  when  it  is  with- 
drawn. When  thoroughly  molten,  or  "hot,"  very  little  or  no 
steel  adheres  to  the  rod,  which  may  even  be  melted  off  at  the 
end.  In  some  of  the  mills,  when  the  steel  is  "  hot"  and  "  quiet, " 
the  melter  throws  envelopes  containing  ferrosilicon  and  ferro- 
manganese  into  the  crucibles,  replacing  the  lids  of  the  crucibles 
and  the  covers  of  the  furnace.  In  a  few  minutes,  the  covers  are 


CRUCIBLE   STEEL  127 

removed  and  the  crucibles  drawn  from  the  furnace  and  poured. 
In  other  mills,  the  crucibles  are  removed  from  the  furnace  as 
soon  as  the  metal  is  in  condition  for  pouring,  and,  after  a  crucible 
has  been  removed  from  the  furnace,  the  slag  collecting  on  the 
surface  of  the  metal  is  first  removed  by  a  long  iron  bar,  and  then 
a  small  amount  of  ferromanganese  is  put  into  the  crucible. 
Whether  the  ferromanganese  is  put  into  the  crucible  before  or 
after  it  is  removed  from  the  furnace  appears  to  be  immaterial, 
inasmuch  as  the  object  of  introducing  this  ingredient  is  merely 
to  oxidize  the  metal  while  it  is  being  poured,  in  order  to  insure 
freedom  from  blow-holes  or  flaws  in  the  ingots.  Other  metals, 
such  as  titanium  and  vanadium,  are  frequently  added  in  small 
amounts  as  final  deoxidizers.  Sometimes  aluminum  is  thrown 
into  the  crucible,  to  make  the  metal  set  quietly  in  the  mold,  but, 
as  a  rule,  this  is  not  required,  if  the  steel  has  been  properly  melted. 

Ingot  Molds.  —  The  ingot  molds  are  made  in  halves.  They 
are  generally  made  from  cast  iron,  and  their  inside  dimensions 
vary.  Often  they  are  about  four  inches  square  by  three  feet 
long.  The  two  parts  of  the  mold  are  held  together  by  rings  and 
wedges,  one  ring  at  the  top  and  one  at  the  bottom,  the  molds 
being  stood  on  end  while  pouring  the  hot  metal  into  them.  It 
is  essential  that  the  finish  on  the  inside  of  these  molds  is  smooth. 
If  the  inside  is  not  smooth,  the  ingot  will  have  a  rough  surface, 
which  may  result  in  difficulties  in  the  finished  bar.  The  joints 
must  also  be  tight,  so  that  the  hot  metal  cannot  work  through 
them  and  form  a  fin  on  the  ingot.  This  fin  would  have  to  be 
removed,  which  would  increase  the  cost  of  manufacture.  If 
it  were  not  removed,  it  would  be  hammered  and  rolled  into  the 
steel  and  cause  imperfections.  In  order  to  prevent  the  steel 
from  sticking  to  the  molds,  the  latter  are  "  smoked"  by  burning 
rosin  or  some  other  heavy,  greasy,  and  smoke-making  material 
underneath  them.  This  leaves  a  thick  black  coat  of  smoke  or 
soot  on  the  face  of  the  molds.  The  molds  should  also  be  warmed 
before  they  are  used. 

Pouring  or  Teeming.  —  The  pouring  or  teeming  is  an  import- 
ant part  of  the  process.  It  is  necessary  to  have  a  steady  stream 
of  metal  enter  the  mold.  If  it  is  stopped  and  started  again, 


128  IRON   AND   STEEL 

there  will  be  an  imperfection  in  the  ingot,  and  a  bar  hammered 
and  rolled  from  it  will  not  be  homogeneous.  In  fact,  the  ingot, 
when  hammered,  is  likely  to  break  at  the  point  where  the  in- 
terruption of  the  stream  occurred.  The  stream  of  hot  metal 
should  not  be  permitted  to  strike  the  side  of  the  mold,  because,  in 
that  case,  it  is  likely  to  cut  the  mold  and  produce  a  rough  ingot. 
Furthermore,  the  mold  will  be  destroyed  in  a  few  heats.  The 
teeming,  therefore,  requires  considerable  practice.  Sometimes 
the  steel  is  not  poured  directly  from  the  crucibles,  but  is  first 


Fig.  3.     Pouring  the  Molten  Steel  into  Molds  to  form 
Ingots  of  Crucible  Steel 

poured  into  ladles,  and  then  into  the  molds.  When  a  ladle  is 
used,  the  pouring  is  easier,  and  this  method  is  considered,  by 
many,  the  better  procedure,  especially  when  uniform  ingots  are 
required,  as  the  metal  from  a  number  of  crucibles  may  be  poured 
into  one  large  ladle;  hence  a  more  homogeneous  mixture  is  ob- 
tained. Fig.  3  illustrates  how  the  molten  steel  is  poured  into 
the  vertical  molds. 

When  clay  crucibles  are  used,  as  soon  as  the  metal  has  been 
poured,  the  crucible,  which  is  not  permitted  to  cool  off  because 
it  would  be  destroyed  by  cracking,  is  put  back  into  the  furnace 
to  be  heated  up  again  before  recharging.  In  some  cases,  when 


CRUCIBLE   STEEL  1 29 

it  has  not  cooled  off  too  much  during  the  pouring,  it  will  be  im- 
mediately recharged  without  reheating.  When  reheated,  how- 
ever, it  is  removed  from  the  furnace  after  a  few  minutes,  and  the 
charge  put  into  it  as  already  described.  It  is  then  immediately 
put  back  into  the  furnace  where  it  is  permitted  to  remain  from 
four  to  six  hours,  when  it  is  again  removed,  and  the  metal  poured, 
and  the  same  process  repeated.  When  a  furnace  is  in  operation 
day  and  night,  about  five  heats  are  generally  obtained  in  the 
course  of  twenty-four  hours.  A  clay  crucible  will  only  last  for 
about  from  four  to  six  heats. 

Piping.  —  One  of  the  greatest  difficulties  in  making  crucible 
steel  ingots  is  due  to  " piping";  that  is,  the  formation  of  a  spongy 
mass  or  even  a  hole  at  the  center  of  the  ingot.  Piping  is  caused 
by  the  side  of  the  ingot  cooling  faster  than  the  central  part. 
As  the  metal  in  the  ingot  cools  and  solidifies  toward  the  sides, 
the  still  molten  metal  at  the  center  separates  and  a  "pipe" 
forms.  There  is  a  greater  tendency  for  a  pipe  to  form  at  the 
top  of  the  ingot  than  farther  down,  because  a  tendency  for  a 
pipe  to  form  in  the  lower  part  is  offset  by  the  metal  from  the 
upper  part  of  the  ingot  filling  the  space  formed.  The  most 
general  method  for  avoiding  piping  in  crucible  steel  is  by  the 
use  of  so-called  "hot  tops."  A  "hot  top"  is  a  brick  made  of 
fireclay  with  a  hole  through  it,  the  size  of  the  brick  and  the  hole 
depending  upon  the  size  of  the  ingot.  The  method  of  using  a 
hot  top  is  described  by  George  H.  Heilson,  in  an  address  before 
the  Engineering  Society  of  Western  Pennsylvania,  as  follows: 
When  the  mold  has  been  almost  filled,  the  hot  top  is  placed  on 
top  of  the  hot  steel  in  the  mold  and  the  hole  filled  with  the 
melted  steeL  This  plug,  as  it  may  be  called,  settles  into  the 
pipe  as  it  develops,  and  also  has  a  tendency  to  keep  the  top  of 
the  ingot  hot  and  thus  lessen  the  pipe.  The  hot  top,  however, 
does  not  prevent  the  formation  of  small  cavities  below  the  main 
portion  of  the  pipe.  It  should  be  remembered  that  the  hot  top 
brick  must  be  heated  to  as  high  a  temperature  as  it  will  stand 
before  being  placed  on  the  ingot.  If  this  is  not  done,  the  cold 
brick  will  chill  the  steel  and  destroy  the  usefulness  of  the  hot  top. 
When  the  ingots  are  cold,  the  top  is  broken  off  so  that  a  clean 


130  IRON  AND   STEEL 

fracture  is  obtained,  which  is  used  for  judging  the  carbon  con- 
tent. 

Welding  Process.  —  After  the  ingot  has  been  poured  in  the 
mold,  it  is  permitted  to  cool  off,  after  which  it  is  removed  from 
the  mold.  The  next  operation  performed  is  the  heating  of  the 
ingots  in  a  furnace  to  a  welding  or  white  heat,  after  which  they 
are  put  through  what  is  termed  the  " welding''  process.  This 
consists  in  placing  the  white-hot  ingot  under  the  steam  hammer 
and  lightly  tapping  it^with  gentle  blows  on  the  surface  so  as  to 
close  up  or  weld  all  minute  cracks  or  flaws  that  may  be  present 
on  the  outside  of  the  ingot.  This  insures  a  homogeneous  struc- 
ture and  freedom  from  flaws  and  cracks  in  the  finished  material. 
The  welding  process  is  not  always  carried  out,  as  it  is  considered 
unnecessary  when  ingots  are  poured  in  very  smooth  molds. 

Hammering  the  Bars  to  Size.  —  The  ingot  may  be  reduced 
to  its  required  size  and  shape  either  by  hammering  or  by  rolling. 
Those  bars  that  are  hammered  to  the  required  size  are  either  per- 
mitted to  cool  down,  after  having  been  welded,  and  are  then  re- 
heated to  a  red  heat,  or  they  may  be  immediately  taken  from 
the  steam  hammer,  where  the  welding  was  done,  and  placed  under 
the  steam  hammer  where  they  are  to  be  hammered  to  size.  The 
hammering  adds  to  the  firmness  and  quality  of  the  steel,  and  in- 
sures homogeneity  of  the  material.  In  order  to  insure  the  cor- 
rect size  being  obtained,  tools  similar  to  those  employed  by 
regular  blacksmiths  are  used  as  stops  and  gages.  A  square 
block  provided  with  a  long  shank,  called  a  "peg,"  is  placed  on 
the  anvil  of  the  hammer  and  acts  as  a  stop.  (Several  of  these 
blocks  are  shown  in  Fig.  4.)  This  block  has  a  thickness  equal  to 
the  required  thickness  or  diameter  of  the  bar.  When  the  steam 
hammer  has  hammered  down  the  bar  to  this  size,  it  will  strike 
this  block,  and  is  thus  prevented  from  making  the  bar  under 
size.  After  the  bar  has  been  thus  hammered  down  to  a  given 
size,  by  using  the  pegs  as  stops,  it  is  gaged  by  sheet-iron  snap 
gages  at  various  places,  in  order  to  ascertain  that  it  is  of  the 
correct  size  uniformly  along  its  whole  length.  For  round  bars, 
swages  similar  to  those  used  by  the  ordinary  blacksmith  are 
employed  to  obtain  a  round  and  smooth  surface.  When  the 


CRUCIBLE   STEEL  131 

bars  have  been  hammered  down  to  the  correct  size,  they  are  an- 
nealed in  order  that  they  may  be  soft  enough  for  working.  The 
annealing  furnace  generally  contains  a  number  of  long  large 
pipes;  they  may  be  regular  cast-iron  water  or  gas  pipes.  The 


Fig.  4. 


A  Collection  of  Tools  used  when  Handling  Crucible 
Steel  Ingots  and  Hammering  them  to  Size 


bars  are  placed  in  these  pipes  and  the  ends  of  the  pipes  are  sealed 
with  fireclay.  After  this,  the  front  of  the  furnace  is  closed 
by  a  cover  and  it  is  heated  for  about  twenty-four  hours.  Then 
the  fire  is  deadened,  and  the  bars  are  permitted  to  cool  slowly  for 
about  two  days;  they  are  then  ready  for  the  market. 


132 


IRON   AND    STEEL 


Rolling  the  Bars.  —  Small  sizes  of  square  and  round  stock  are 
generally  not  hammered  into  shape,  but  are  rolled  to  the  re- 
quired size.  The  ingot  is  first  heated  to  a  high  heat  and  is  then 
placed  between  the  first  set  of  rolls,  after  which  it  passes  between 
the  rolls  from  one  side  to  the  other,  becoming  smaller  in  cross- 
section  and  of  greater  length  at  each  successive  pass.  When  the 

"Carbon-temper"  of  Steel 

(JOSEPH  T.  RYERSON  &  SON) 


Temper 
Number 


Per  Cent 
Carbon 


Tools  for  which  Steel  is  Adapted 


0.65  to  0.75 

0.75  to  0.85 

0.85  to  0.95 
0.95  to  i  .05 

1.05  to  1.15 

.15  tD  I.2S 

1.25  to  1.35 

1.35  to  1.45 
1.45  to  1.55 


(  Blacksmith's  hammers,  table  knives,  dies  for 
drop  hammers,  large  hot  forgings,  flatten;, 
(     fullers,  track  chisels,  and  tools. 

(  Large   shear  knives,  punches,  chisels,  ham- 
mers,  boilers,   boiler-makers'  tools,    lathe 
C      centers,  etc. 

(  Punches  and  dies,  hand  chisels,  mining  tools, 
(  shear  blades,  etc. 

(  Drills,  large  milling  cutters,  axes,  taps,  ream- 
I  ers,  bolt  header  dies,  and  similar  tools. 

(  Granite  chisels,  milling  cutters,  taps,  ream- 
ers, mill  picks,  threading  dies,  cups,  cones, 
(      etc. 

(  Milling  cutters,  small  taps,  threading  dies, 
twist  drills,  forming  and  boring  tools,  man- 
(      drels,  razors. 

C  Inserted  milling  cutter  teeth,  lathe,  planer 
and  slotter  tools  and  tools'  requiring  great 
(      hardness. 

(  Cutting  disks,  granite  lathe  tools,  paper 
<  knives,  engravers'  tools,  roll  corrugating 
(  and  chilled  roll  turning  tools. 

Steel  for  turning  chilled  rolls,  etc.,  requiring 
great  hardness. 


ingots  are  to  be  rolled  down  to  very  small  sizes,  the  work  is  done 
in  two  stages,  owing  to  the  great  length  of  the  bar  when  it  has 
been  rolled  down  to  a  comparatively  small  size.  In  such  cases, 
the  bar,  after  having  been  rolled  down  to  a  certain  size  is  cut  up 
under  shears  into  shorter  pieces  of  equal  length,  immediately 
after  coming  from  the  rolls.  These  pieces  are  then  reheated  in 


CRUCIBLE   STEEL  133 

the  furnace  and  are  again  rolled  to  produce  smaller  sizes. 

Crucible  steel  ingots  should  be  handled  with  great  care  in 
heating  for  rolling  and  hammering.  The  flame  of  the  heating 
furnace  must  not  be  strongly  oxidizing,  and  the  ingots  should 
be  brought  to  the  forging  or  rolling  heat  very  slowly.  The  re- 
duction in  rolling  must  be  small  compared  with  the  practice 
followed  for  commercial  Bessemer  or  open-hearth  steels.  Cru- 
cible steel  cannot  be  handled  in  the  same  way.  As  an  illustra- 
tion, in  reducing  a  3-inch  square  billet  of  open-hearth  steel  to 
|  inch  round,  there  would  be,  perhaps,  14  passes  through  a  mill 
driven  at  a  high  speed.  With  crucible  steel,  there  would  be 
21  passes  through  a  mill  driven  at  a  much  slower  speed. 

Grades  of  Crucible  Steel.  —  Crucible  steel  is  graded  according 
to  its  "  temper,"  the  term  "  temper"  or  "  carbon- temper "  being 
used  by  steel-makers  to  indicate  the  amount  of  carbon  in  the  steel. 
"  One"  temper  is  generally  taken  to  mean  o.io  per  cent  of  carbon. 
This  designation,  however,  for  the  percentage  of  carbon  varies 
with  different  makers.  The  accompanying  table  gives  a  list 
of  tempers  and  the  purposes  for  which  the  various  steels  of 
given  temper  number  are  adapted,  as  listed  by  one  dealer. 

To  assist  in  their  grading,  as  the  bars  have  been  hammered 
to  size  from  the  ingots,  they  are  nicked  on  all  sides  with  a  tri- 
angular tool  at  what  was  the  upper  end  of  the  ingot.  After  they 
are  cold,  the  end  pieces  are  broken  off.  The  appearance  of  this 
fracture  indicates  the  amount  of  carbon  in  the  steel,  and  it  is 
claimed  that  a  trained  inspector  can  tell  from  the  fracture  the 
carbon  content  of  the  steel  within  0.05  per  cent. 

The  best  all-around  tool  steel  contains  from  0.90  to  i.io  per 
cent  of  carbon,  and  can  be  adapted  to  a  wider  range  of  uses  than 
any  other  grade.  For  tools,  generally,  it  gives  the  highest 
strength  together  with  a  high  degree  of  hardness  when  heat- 
treated.  It  cannot,  however,  be  welded  easily.  Steels  con- 
taining up  to  1.50  per  cent  of  carbon  are  easily  burnt,  and  are 
welded  only  with  great  difficulty.  They  can,  however,  be 
hardened  to  an  extreme  hardness.  When  the  carbon  content  is 
0.75  per  cent,  the  steel  is  more  easy  to  weld,  but  will  not  become 
very  hard  when  heat-treated. 


CHAPTER  VII 
THE  BESSEMER  PROCESS 

NOTWITHSTANDING  the  high  cost  of  making  steel  by  the  crucible 
process,  no  more  satisfactory  method  was  developed  until  1855. 
In  that  year,  Sir  Henry  Bessemer  patented  a  method  of  producing 
steel  by  blowing  air  through  molten  pig  iron,  and  in  this  way  re- 
ducing the  carbon,  silicon,  and  manganese  content  by  burning 
out  the  greater  amount  of  these  constituents.  The  metal  first 
produced  by  the  Bessemer  process,  as  originally  applied,  was 
a  nearly  carbonless  iron,  but  the  iron  obtained  from  the  early 
experiments  produced  ingots  that  were  full  of  blow-holes  and 
which  could  not  be  used  commercially.  For  some  time,  therefore, 
the  process  was  merely  used  for  burning  out  the  carbon  from  pig 
iron.  The  molten  metal  was  then  granulated  by  being  poured, 
while  in  the  molten  state,  into  water,  after  which  it  was  converted 
into  steel  by  the  crucible  process.  Later,  however,  the  process 
was  improved  so  that  steel  could  be  made  directly  in  the  converter 
by  first  burning  out  the  carbon  as  explained,  and  then  adding 
the  required  amount  of  manganese  and  carbon  to  produce  a 
steel  with  a  definite  carbon  content.  This  invention  so  reduced 
the  cost  of  steel  that  it  is  doubtful  if  any  other  invention  or  dis- 
covery has  had  so  large  an  influence  on  industry  and  manufac- 
turing in  general.  Furthermore,  the  Bessemer  process  makes 
available  for  use  in  steel-making  large  deposits  of  iron  ore  that 
are  not  suitable  for  the  crucible  process.  For  the  better  grades  of 
steel,  however,  the  Bessemer  process  has  been  replaced  largely 
by  the  open-hearth  process. 

Tonnage  Produced  by  Bessemer  and  Open-hearth  Processes. 

-Prior  to  1908,  more  steel  was  produced  in  the  United  States 

by  the  Bessemer  process  than  by  the  open-hearth  process,  but 

since  that  time  the  use  of  open-hearth  steel  has  increased  greatly. 

The  following  figures,  which  represent  the  gross  tons  produced 

134 


BESSEMER  PROCESS 


135 


in  the  United  States,  indicate  the  relative  importance  of  the 
Bessemer  and  open-hearth  processes  at  different  periods.  In 
1880,  the  Bessemer  tonnage  was  1,074,260  and  the  open-hearth, 
100,850;  in  1890,  Bessemer,  3,688,870,  open-hearth,  513,230; 
in  1900,  Bessemer,  6,684,770,  open-hearth,  3,398,135;  in  1907, 
the  Bessemer  and  open-hearth  tonnages  were  approximately 


Fig.  i.     A  Bessemer  Converter 

equal;  in  1910,  the  Bessemer  tonnage  was  9,412,770,  as  compared 
with  16,504,510  for  the  open-hearth  process.  In  1916,  nearly 
three  times  the  tonnage  was  produced  by  the  open-hearth  process, 
tfye  figures  being  for  the  Bessemer,  11,059,040,  and  for  the  open- 
hearth,  31,415,430. 

Principle  of  the  Bessemer  Process.  —  Briefly  described,  the 
Bessemer  process  for  making  steel  consists  in  putting  molten 
pig  iron  in  a  large  pear-shaped  vessel  called  a  converter  (see  Fig. 


i36 


IRON  AND    STEEL 


i),  in  which  the  carbon  and  other  impurities  are  oxidized  and  re- 
moved by  blowing  air  up  through  the  molten  mass.  The  air  is 
unheated  and  has  sufficient  pressure  to  prevent  the  molten  metal 
from  entering  the  tuyeres  through  which  the  air  is  blown.  The 
required  pressure  is  about  twenty  pounds  per  square  inch. 
The  molten  iron  is  poured  into  the  converter  in  quantities  of 
from  ten  to  twenty  tons  at  a  time  directly  from  the  blast  fur- 
nace, while  the  converter  is  in  a  horizontal  position.  Then  the 


Fig.  2.     A  Bessemer  Converter  Pouring 

compressed  air  is  turned  on  as  the  converter  is  raised  to  a  ver- 
tical position.  When  the  carbon,  silicon,  and  other  elements 
have  been  practically  burned  out,  which  requires  less  than  ten 
minutes,  the  converter  is  again  turned  to  the  horizontal  position, 
the  blast  is  shut  off,  and  the  proper  carbon  content  is  given  to  the 
steel  to  be  made  by  recarburizing  the  mass  of  molten  metal  by 
adding  spiegeleisen  or  ferromanganese.  These  are  added  in 
liquid  form,  and  after  these  ingredients  have  properly  been  taken 
up  by  the  molten  metal,  the  liquid  steel  is  poured  into  ingot 
molds,  and  the  ingots,  while  still  hot,  are  rolled  into  blooms, 


BESSEMER   PROCESS  137 

billets,  or  rails,  without  additional  reheating,  except  for  a  short 
period  in  a  so-called  "  soaking  pit. "  The  molten  metal  may  also 
be  cast  directly  into  steel  castings.  Fig  2  shows  the  metal  being 
poured  from  a  Bessemer  converter. 

There  are  two  specific  Bessemer  processes  in  use,  one  known 
as  the  acid  Bessemer  process  and  the  other  as  the  basic  Bessemer 
process.  In  the  acid  process,  the  converter  lining  is  made  of 
refractory  acid  materials  composed  principally  of  silica,  so  that 
the  phosphorus  and  sulphur  content  in  the  charge  of  molten 
metal  remains  unreduced.  The  acid  process  is  generally  used 
in  the  United  States,  there  being  a  sufficient  supply  of  low  phos- 
phorus and  sulphur  ores  to  employ  this  process  almost  exclusively. 
Steel  of  a  fair  quality  is  produced  by  this  process  at  low  cost  and 
with  great  rapidity.  In  the  basic  process,  the  converter  is  lined 
with  burnt  dolomite,  and  lime  is  added  to  the  charge  of  molten 
metaPto  reduce  the  phosphorus  and  sulphur.  This  process  is 
used  only  when  so-called  ll Bessemer  ores,"  low  in  phosphorus, 
are  not  available. 

The  Converter.  —  The  converter  in  which  the  blowing  oper- 
ation is  carried  on  consists  of  a  casing  of  thick  iron  plates 
lined  with  refractory  material  and  supported  by  trunnions. 
Air  from  a  blast  pipe  is  admitted  through  one  of  the  trunnions, 
and  a  pinion  is  keyed  to  the  other.  A  hydraulic  ram  geared  to 
this  pinion  turns  the  converter  into  a  horizontal  position  for 
charging  and  discharging,  and  into  an  upright  position  for  blow- 
ing. In  most  steel-making  mills,  the  air  passes  from  the  trun- 
nion to  a  wind-box  at  the  bottom  of  the  converter,  and  then 
through  the  tuyeres  into  the  vessel.  In  the  steel  foundry  and 
some  places  making  only  a  small  quantity  of  steel,  side-blown 
converters  are  used,  but,  in  either  case,  the  process  is  the  same; 
the  principal  difference  is  in  the  amount  of  steel  made. 

In  the  bottom-blown  converter,  the  wind-box  is  of  cast-iron, 
and  is  easily  removed  and  taken  apart.  The  tuyeres,  too,  may 
be  quickly  removed  from  the  converter,  as  the  entire  bottom  is 
held  to  the  vessel  by  hooks  and  links.  The  tuyeres  are  cylin- 
drical clay  bricks  that  extend  from  the  plate  covering  the  wind- 
box  to  the  surface  of  the  refractory  bottom;  each  brick  is  pierced 

9F 


138  IRON  AND   STEEL 

with  a  number  of  openings.  Enough  tuyeres  are  provided  so 
that  the  combined  area  of  their  openings  is  about  2.5  square 
inches  for  each  ton  of  charge.  If  large  openings  and  a  rather  low 
blast  pressure  are  used,  the  air  passes  through  the  bath  in  large 
bubbles.  Small  openings  and  a  pressure  of  from  10  to  30  pounds 
per  square  inch  cause  the  air  to  be  broken  into  spray  and  so 
brought  into  more  intimate  contact  with  the  metal. 

Converters  may  have  a  concentric  or  an  eccentric  nose.  Many 
steel-makers  prefer  a  nose  that  is  fixed  at  an  angle  of  about  30 
degrees  with  the  body;  the  straight-  or  concentric-nose  vessel, 
however,  is  generally  preferred,  as  it  is  claimed  that  it  does  not 
"slop"  as  much  as  the  other;  that  is,  less  metal  is  thrown  out 
of  the  converters  by  the  violence  of  the  action.  In  either  form, 
the  modern  converters  generally  hold  about  twenty  tons  of 
molten  metal. 

Converter  Linings.  —  In  American  practice,  the  converter  is 
commonly  lined  with  ganister  or  silica  brick,  which  forms  what 
what  is  known  as  an  acid  lining.  Steel  made  in  these  converters 
is  known  as  acid  steel,  and  the  process  is  then  spoken  of  as  the 
acid  process.  This  lining  is  about  12  inches  thick  and  lasts  from 
three  to  five  months,  or  for  from  3000  to  5000  heats.  The 
bottom,  however,  only  lasts  for  from  30  to  35  heats,  as  a  rule, 
owing  to  the  intense  heat  at  the  ends  of  the  tuyeres.  It  is  made 
of  ganister  rocks  and  clay,  or  by  filling  the  spaces  around  the 
tuyeres  with  large  bricks  set  on  end  and  tamping  ganister  in 
the  interstices  with  molders'  rammers.  The  bottom  may  be 
from  26  to  30  inches  thick.  As  soon  as  it  is  made,  it  is  placed 
in  ovens  and  thoroughly  dried. 

As  the  bottoms  are  quickly  burned  away,  arrangements  must 
be  made  for  their  quick  and  easy  renewal.  In  some  places,  the 
converter  is  turned  into  a  vertical  position  with  the  bottom  up; 
the  bottom  is  then  removed  by  a  crane  which  also  puts  a  new 
one  in  place.  As  soon  as  this  is  fastened  in  position,  the  con- 
verter is  ready  for  use.  In  other  plants,  a  car  is  run  under  the 
converter  and  raised  against  the  bottom  by  a  hydraulic  lift.  As 
soon  as  the  bottom  is  unfastened  from  the  converter,  the  car  is 
lowered  and  a  car  carrying  a  new  bottom  is  run  upon  the  lift 


BESSEMER  PROCESS  139 

and  raised  into  place.     When  this  bottom  is  fastened  to  the 
converter,  the  lift  is  lowered  and  the  converter  is  ready  for  use. 

Sometimes,  the  lining  consists  of  dolomite.  This  is  known 
as  a  basic  lining,  the  steel  made  in  this  converter  is  known  as 
basic  steel,  and  the  process  is  termed  the  basic  process.  The 
material  for  this  lining,  after  being  burnt  and  ground,  is  mixed 
with  anhydrous  tar  and  made  into  bricks,  which  are  burnt  at  an 
intense  heat.  These  bricks  are  then  laid  with  a  mortar  of  the 
same  material.  Sometimes,  however,  the  lining  is  rammed  into 
place  instead  of  being  laid  in  the  form  of  bricks,  but  the  mixture 
is  the  same  in  either  case.  The  thickness  of  the  lining  varies 
from  12  to  14  inches  at  the  bottom,  to  from  8  to  16  inches  at  the 
nose;  the  bottom  is  from  20  to  26  inches  thick.  The  tuyeres  may 
be  clay  bricks,  as  in  the  acid  converter,  but  quite  generally  are 
simply  holes  left  in  the  bottom  by  ramming  the  clay  around  iron 
pins,  which  are  then  withdrawn.  The  basic  converter  must  be 
larger  than  the  acid,  because  of  the  large  amount  of  slag  and  lirne 
charged,  and  lasts,  on  the  average,  only  for  about  one  hundred 
heats. 

Operation  of  a  Bessemer  Converter.  —  Before  a  converter  is 
put  into  operation,  its  lining  is  brought  to  a  red  heat.  It  is 
then  turned  on  its  side  and  a  charge  of  molten  pig  iron  poured 
in  through  the  mouth.  The  blast  is  turned  on  and  the  vessel  is 
turned  into  a  more  nearly  vertical  position.  As  the  violence  of 
the  blow  increases,  the  vessel  is  gradually  turned  until  it  is  nearly 
vertical. 

When  the  converter  is  first  turned  up,  all  the  oxygen  of  the 
blast  is  consumed  in  the  oxidation  of  silicon  and  manganese  so 
that  only  the  nitrogen  passes  through  the  metal.  The  graphi- 
tic carbon  is  burned  into  the  combined  form,  and  the  silicon  is 
oxidized  to  silica;  this  combines  with  the  oxides  of  iron  and 
manganese  to  form  slag.  There  issues  from  the  mouth  of  the 
vessel,  therefore,  only  sparks  and  small  particles  of  slag  and  no 
true  flame  is  formed.  When  the  silicon  and  manganese  are  nearly 
gone,  the  carbon  begins  to  burn.  It  is  converted  into  carbon 
monoxide  by  the  blast,  and  as  this  passes  through  the  vessel 
with  the  nitrogen,  it  ignites  at  the  mouth,  producing  an  in- 


140  IRON  AND   STEEL 

tensely  bright  flame.  This  stage  of  the  process,  which  is  known 
as  the  "boil,"  is  equivalent  to  the  boiling  stage  of  the  puddling 
process.  As  the  escape  of  large  quantities  of  carbon  monoxide 
produced  by  the  oxidation  of  the  carbon  by  the  blast  causes  a 
violent  agitation  of  the  metal,  the  blast  is  now  reduced.  While 
at  first  it  is  small,  the  flame  rapidly  increases  in  size  until  it 
reaches  its  full  height.  When  all  the  carbon  is  burned,  the 
flame  drops  quite  sharply,  which  is  a  sign  that  the  process  is 
complete. 

The  heat  produced  by  the  combustion  of  the  silicon  to  silica 
and  of  the  manganese  to  manganese  oxide  keeps  the  molten  metal 
fluid  until  all  the  impurities  are  removed  and  a  bath  of  molten 
iron  remains.  Iron  is  burned  to  a  certain  extent  throughout 
the  process,  but  when  the  carbon,  silicon,  and  manganese  are 
nearly  eliminated,  the  oxidation  of  iron  becomes  considerable. 
The  resulting  oxide  of  iron  is  absorbed  by  the  molten  bath  and 
is  chiefly  responsible  for  the  tendency  to  uwildness, "  shown  by 
Bessemer-blown  metal. 

As  soon  as  the  flame  drops,  the  blast  is  shut  off,  the  vessel  is 
turned  on  its  side,  and  a  recarburizer  is  added  to  the  charge. 
The  manganese  in  this  reduces  the  dissolved  oxide  of  iron  and 
burns  the  sulphur  (which  is  in  the  form  of  iron  sulphide)  into 
manganese  sulphide.  A  part  of  this  floats  to  the  surface  of  the 
bath,  where  the  sulphur  is  largely  volatilized  as  sulphur  dioxide, 
but  a  part  remains  suspended  in  the  metal. 

Control  of  Conversion  Process.  —  The  Bessemer  process  dif- 
fe^from^alLother  steel-making  processesby  requiring  no  heat 
from  some  outside  sourcefor  its  operation.  All  thelieat  "heces- 
sary  is  furnished  by  tfoToxIcIation  through"  the  blast.  In  the 
acid  process,  the  heat  is  obtained  mostly  by  regulating  the  amount 
of  silicon  in  the  charge,  about  0.25  per  cent  usually  being  suffi- 
cient. Should  any  blow  become  too  hot,  it  is  cooled  by  throw- 
ing into  the  converter  scrap  steel,  such  as  the  waste  ends  of 
rails  and  other  pieces.  Sometimes,  as  when  enough  scrap  steel 
has  not  been  thrown  into  the  bath,  steam  is  blown  in  with  the 
blast.  The  dissociation  of  this  into  its  component  parts,  oxygen 
and  hydrogen,  requires  so  much  heat  that  the  metal  is  cooled 


BESSEMER   PROCESS  141 

considerably  as  the  heat  is  absorbed  from  the  metal.  Many 
mills  prefer  the  method  of  cooling  by  the  use  of  steam,  because  it 
eliminates  the  handling  of  scrap  and  also  permits  the  scrap  to 
be  used  in  the  open-hearth  process,  which  is  a  more  economical 
practice. 

Should  the  bath  become  too  cold,  the  temperature  may  be 
raised  by  tipping  the  vessel  forward  until  one  or  more  of  the 
tuyeres  comes  close  to,  or  just  above,  the  surface  of  the  metal. 
It  then  oxidizes  the  iron  which  is  at  once  absorbed  by  the  slag; 
the  heat  of  this  oxidation  greatly  increases  the  temperature  of 
the  metal.  Besides,  the  air  burns  some  of  the  carbon  monoxide 
to  carbon  dioxide  inside  of  the  vessel,  which  action  also  develops 
heat. 

In  the  basic  process,  the  heat  is  furnished  by  the  phosphorus, 
so  that  pig  iron  high  in  this  element  must  be  used.  Silicon  can- 
noTbe  used,  because  most  of  the  heat  generated  by  its  oxide  is 
consumed  in  heating  the  lime  needed  for  neutralizing  the  re- 
sultant silica. 

Effect  of  Raw  Material  on  Action  of  Converter.  —  In  Ameri- 
can practice,  the  heats  are  blown  in  less  than  ten  minutes,  be- 
cause of  the  small  amount  of  impurities  to  be  oxidized.  As  the 
manganese  in  the  pig  iron  is  low,  the  slag  consists  largely  of 
silicate  of  iron  and  is  quite  sticky.  An  increase  of  manganese  in 
the  pig  iron  increases  the  proportion  of  oxide  of  manganese  in 
the  slag  and  makes  it  more  fluid.  Should  it  be  too  fluid,  it 
may  slop  over  the  mouth  of  the  vessel,  but  this  may  be  prevented 
by  reducing  the  blast  pressure. 

In  Sweden,  where  small  converters  are  quite  generally  used, 
the  manganese  in  the  pig  iron  frequently  exceeds  the  silicon  to 
such  an  extent  that  the  heat  of  combustion  of  the  manganese  is 
largely  substituted  for  that  of  silicon,  and  very  watery  slags  are 
made.  These  slags  are  more  severe  upon  Imings  than  the  more 
siliceous  slags  used  in  America.  When  these  high  manganese 
pig  irons  are  blown,  the  carbon  starts  to  burn  before  all  the 
manganese  is  eliminated;  and  as  the  blowing  is  stopped  when  the 
metal  contains  about  the  amount  of  carbon  desired  in  the  finished 
steel,  enough  manganese  is  obtained  to  make  the  addition  of 


142  IRON  AND   STEEL 

large  amounts  of  spiegeleisen  or  ferromanganese  unnecessary. 
The  uncertainty  of  this  method,  however,  has  not  commended 
its  use  in  other  countries. 

Recarburizing  the  Metal.  —  Owing  to  the  difficulty  of  stop 
ping  the  blow  when  the  charge  contains  the  exact  amount  of 
carbon  and  other  constituents  desired,  the  American  practice  is 
to  continue  the  blow  until  a  decarburized  metal,  known  as  ' '  burnt 
iron,"  is  obtained.  The  proper  amounts  of  the  various  elements 
are  then  added  to  give  the  steel  the  desired  strength  and  quality 
as  well  as  to  enable  it  to  be  handled  in  the  subsequent  operations 
of  casting,  rolling,  forging,  etc.  These  additions  also  remove 
from  the  metal  such  impurities  as  hydrogen,  nitrogen,  and  car- 
bon monoxide,  which  render  the  iron  "wild"  (that  is,  cause 
violent  ebulition  of  the  metal  in  the  furnace,  ladle,  or  mold) 
so  that  the  ingots  are  full  of  blow-holes  and  unfit  for  use.  The 
making  of  these  additions  is  termed  recarburizing. 

The  recarburizers  generally  used  are  ferromanganese,  spiegel- 
eisen, ferrosilicon,  silico-spiegel,  and  carbide  of  silicon.  Ferro- 
manganese is  an  alloy  of  manganese,  iron,  and  carbon;  spiegel- 
eisen is  the  same,  except  that  it  contains  less  than  25  per  cent  of 
manganese.  Ferrosilicon  is  a  very  high  silicon  pig  iron.  Silico- 
spiegel  is  a  very  high  silicon  spiegeleisen  or  a  very  high  manga- 
nese ferrosilicon.  These  four  are  made  in  a  regular  iron  blast 
furnace  from  properly  selected  ores  and  with  special  manipula- 
tion of  the  furnace.  Carbide  of  silicon  (carborundum)  is  an 
alloy  of  carbon  and  silicon  produced  in  the  electric  furnace. 
It  has  been  used  for  only  a  few  years  and  has  the  advantage  that 
a  smaller  amount  is  required  for  the  same  increase  in  silicon  or 
carbon,  and  that  the  temperature  of  the  steel  is  increased  instead 
of  lowered  as  is  the  case  with  the  metallic  alloys.  This  increase 
in  temperature  is  due  partly  to  heat  developed  by  the  combustion 
of  silicon  and  carbon,  but  mainly  to  the  fact  that  the  decompo- 
sition of  the  compound  releases  a  large  amount  of  heat. 

Sometimes  metallic  aluminum  is  used  to  quiet  the  steel,  as  it 
acts  as  a  deoxidizer.  While  a  given  amount  of  silicon  will 
combine  with  more  oxygen  than  the  same  amount  of  aluminum, 
the  latter  has  a  much  greater  affinity  for  oxygen  under  the 


BESSEMER  PROCESS  143 

conditions  and  is,  therefore,  the  more  powerful  deoxidizer.  Be- 
sides removing  gases  and  making  the  steel  quiet,  it  rapidly  per- 
meates the  entire  mass  of  the  steel,  causing  the  other  elements 
to  blow  more  uniformly,  thus  preventing  or  lessening  segrega- 
tion. The  addition  of  aluminum  also  gives  sounder  ingot  tops, 
thus  lessening  the  loss  in  the  scrap  and  slightly  increasing  the 
strength  of  the  steel. 

Methods  of  Recarburizing.  —  When  only  small  amounts  of 
recarburizer  are  being  added  to  a  large  heat,  the  addition  is 
thrown  into  the  ladle  as  the  molten  metal  is  being  poured;  but 
when  much  recarburizing  material  is  to  be  added,  the  recarbur- 
izer is  melted  in  a  small  cupola  and  poured  into  the  converter. 
In  this  case,  a  low  blast  is  turned  on  for  a  few  seconds  to  thor- 
oughly mix  the  recarburizer  with  the  metal,  but  the  blast  is  not 
left  on  long  enough  to  cause  any  loss  by  the  blast.  Aluminum 
and  carbide  of  silicon  are  always  added  in  the  ladle;  the  latter 
produces  a  violent  reaction  if  very  much  is  used. 

When  the  alloys  do  not  give  the  necessary  amount  of  carbon 
but  do  provide  sufficient  manganese,  solid  carbon  in  the  form  of 
crushed  coke  or  anthracite  is  sometimes  put  into  the  ladle; 
this  is  known  as  the  " Darby  method  of  recarburizing."  The 
coke  or  coal  is  placed  and  weighed  in  ordinary  paper  sacks  that 
contain  enough  material  to  add  o.oi  or  0.02  per  cent  of  carbon 
to  the  steel.  The  amount  of  carbon  absorbed  by  the  steel  de- 
pends upon  the  condition  of  the  bath,  the  amount  increasing 
with  the  temperature.  About  44  per  cent  of  the  best  anthracite 
used  for  this  purpose  is  pure  carbon;  the  rest  is  ash,  etc. 

Pouring  the  Ingots.  —  As  soon  as  the  blow  is  completed,  the 
metal  is  transferred  to  a  ladle.  A  layer  of  slag  is  usually  poured 
on  top  of  the  metal  to  prevent  the  radiation  of  heat  and  to  pro- 
tect the  metal.  The  converter  is  then  turned  upside  down  with 
the  blast  turned  on,  and  all  slag  thrown  out.  As  soon  as  the 
ingot  molds  are  filled  from  the  ladle,  they  are  covered  with  sand 
to  prevent  loss  of  heat  through  radiation;  and  when  the  iron  has 
hardened  sufficiently,  the  molds  are  removed.  As  the  ingots 
are  too  hot  in  the  interior  to  admit  of  immediate  rolling,  they  are 
placed  in  the  soaking  pits  for  about  an  hour.  By  this  plan,  the 


144  IRON   AND    STEEL 

ingots  are  uniformly  heated  throughout  and  can  be  rolled  with- 
out reheating.  At  one  time,  the  converters  were  arranged  around 
circular  pits  so  that  a  steel  crane  handled  all  ladles,  etc.  The 
present  practice  is  to  pour  the  metal  into  molds  carried  on  cars, 
which  are  then  pushed  to  the  stripper  where  the  molds  are  re- 
moved and  the  ingots  placed  in  the  soaking  pit.  An  electric 
stripper,  used  at  the  Duquesne  Works  of  the  Carnegie  Steel 
Co.,  is  shown  in  Fig.  3. 

Blow-holes. — The  trouble  experienced  with  broken  rails  by  rail- 
roads, especially  in  countries  where  low  temperatures  prevail  in 


Fig  3.     Electric  Stripper  for  Removing  Mold  from  Ingot 

winter,  has  demonstrated  the  necessity  of  producing  sound  rails. 
To  produce  sound  rails  means  that  the  ingots  from  which  the 
rails  are  made  must  also  be  sound.  When  the  molten  steel  is 
poured  into  the  comparatively  cold  molds,  some  of  it  dissolves  or 
occludes  considerable  gas.  This  gas  is  apt  to  remain  in  the  metal 
in  the  form  of  bubbles,  thus  forming  blow-holes  or  honeycombing. 
This  fault  is  greatest  in  the  mildest  steels  and  may  be  mini- 
mized by  the  addition  of  silico-ferromanganese  or  aluminum, 
just  before  the  metal  is  poured  into  the  mold.  These  seem  to 


BESSEMER  PROCESS  145 

deoxidize  the  minute  quantity  of  iron  oxide  and  carbon  monox- 
ide present;  they  also  seem  to  increase  the  solvent  power  of  the 
metal  for  gas,  so  that  even  after  solidification  the  metal  may 
retain  in  solution  the  gas  it  dissolved  when  melted.  Preventing 
the  formation  of  blow-holes,  however,  increases  the  tendency  of 
the  formation  of  a  pipe,  so  that  it  is  often  better  to  permit  these 
holes  to  form,  but  to  control  their  location.  This  may  be  done 
by  limiting  the  amount  of  manganese  and  silicon  the  metal  con- 
tains and  casting  the  steel  at  a  relatively  low  temperature. 

Pipes.  —  As  the  ingot  contracts  in  cooling,  a  conical  depres- 
sion or  cavity  may  be  formed  near  the  top.  This  is  known  as  a 
pipe  and  is  especially  apt  to  occur  in  the  harder  steels.  The 
formation  may  be  partly  prevented  and  the  size  of  the  pipe  de- 
creased by  retarding  the  cooling  of  the  top  part  of  the  ingot  so 
that  the  metal  from  this  part  will  feed  the  pipe  that  tends  to 
form  in  the  lower  part  of  the  mold  as  the  metal  cools.  In  order 
to  confine  the  pipe  to  the  very  end,  the  ingot  should  always  be 
cast  in  an  upright  position  and  not  in  a  horizontal. 

One  method  of  avoiding  piping  is  to  place  charcoal  or  some 
other  combustible  material  on  top  of  the  ingot  mold  after  it  has 
been  filled.  A  layer  of  cupola  slag  should  be  placed  between  the 
charcoal  and  the  molten  steel  in  order  to  protect  the  latter  from 
the  oxidizing  effect  of  a  blast  of  air  which  is  directed  on  top  of 
the  ingot  to  facilitate  the  combustion  of  the  charcoal.  The  ingot 
mold  is  fitted  with  a  sand  top,  holding  a  supply  of  metal  which  is 
kept  in  a  molten  condition  by  the  heat  generated  by  the  charcoal. 
This  molten  metal  descends  in  the  mold  as  contraction  takes 
place,  and  eliminates  any  tendency  toward  piping  which  would 
otherwise  result  from  the  contraction  that  takes  place  during 
cooling. 

Segregation.  —  A  third  defect  is  due  to  the  different  melting 
temperatures  of  the  constituents  of  the  steel.  As  the  ingots  cool, 
the  various  elements  tend  to  separate.  This  fault  is  known  as 
segregation  and  is  greatest  when  the  ingot  is  cooled  slowly. 
Segregation  may  be  briefly  described  as  the  tendency  for  ob- 
jectionable impurities  in  steel  —  particularly  sulphur  and  phos- 
phorus —  to  be  concentrated  at  the  center  of  the  ingot.  The 


146 


IRON  AND  STEEL 


material  constituting  such  segregated  sections  is  defective  in 
strength,  and  when  rails  or  structural  material  are  rolled  from 
ingots  containing  such  defects,  the  strength  of  the  resulting 
product  is  seriously  impaired.  As  the  inner  portions  are  the 
last  to  solidify,  there  is  a  tendency  for  the  sulphur  and  phos- 
phorus to  be  concentrated  in  these  sections. 

Segregation  often  causes  the  impurities  to  settle  around  the 
lower  part  of  the  pipe.  Under  certain  conditions,  this  tendency 
should  be  promoted  rather  than  restrained;  then  the  ingots  may 


'Jl>  tjfeiis  ^Hj^    ^SB 

i  mm  I  mm  JMMP> 

I     m*  SSP          *mgmmmf   ••.     mmm-     -  - 


Fig.  4.   Lowering  a  Steel  Ingot  into  a  Blooming  Mill  Soaking  Pit  for 
Reheating  Prior  to  Rolling 

be  made  longer  than  desired  and  the  pipe  part  with  the  blow- 
holes, pipe,  and  segregated  material  may  be  cut  off  and  scrapped 
for  remelting. 

Soaking  Pits.  —  As  the  outside  of  the  ingot  cools  more  rapidly 
than  the  inside,  the  inside  may  be  too  hot  to  be  rolled  or  ham- 
mered when  the  outside  is  hard.  The  ingot  must,  therefore, 
be  brought  to  a  uniform  heat,  which  is  done  by  placing  it  in  the 


BESSEMER   PROCESS  147 

soaking  pit  (see  Fig.  4).  This  is  a  covered  brick-lined  well  in 
which  the  ingot  is  stood  on  end.  It  retains  the  heat  of  previous 
ingots,  so  that  the  excess  of  heat  in  the  interior  of  the  ingot 
placed  in  it  soaks  through  the  mass  but  is  not  lost.  As  a  result, 
the  steel  is  prepared  for  the  mill  without  the  consumption  of  any 
fuel.  In  addition,  the  waste  of  iron  due  to  oxidation  of  the 
outer  crust  of  the  ingot  is  very  slight,  because  the  little  atmos- 
pheric oxygen  in  the  pit  at  the  beginning  is  not  renewed  as  it  is 
in  a  furnace.  Later  forms  of  soaking  pits,  however,  are  heated  by 
regenerative  furnaces,  so  as  to  give  greater  flexibility  to  the 
system.  In  one  plant  the  soaking  pit  consists  of  four  holes,  in 
each  of  which  six  ingots  may  be  placed  at  one  time. 

Basic  Bessemer  Process.  —  As  neither  sulphur  nor  phos- 
phorus is  removed  from  the  steel  in  the  acid  process,  the  pig  iron 
used  must  not  contain  more  than  o.io  per  cent  of  these  impurities. 
At  the  same  time,  the  pig  iron  should  contain  about  2.50  per  cent 
of  silicon,  as  the  high  temperature  is  obtained  mainly  by  the 
combustion  and  oxidation  of  this  element.  What  is  known  as 
Bessemer  pig  iron  is,  therefore,  smelted  from  hematite  ores 
nearly  free  from  phosphorus  and  sulphur.  In  order  that  the 
Bessemer  process  may  be  used  for  the  phosphoric  pig  iron  that 
was  abundant  in  Europe,  Sydney  Thomas  and  Percy  C.  Gil- 
christ,  in  1878,  successfully  developed  the  basic  process.,  which  is 
also  known  as  the  Thomas-Gilchrist  process.  In  this  process",  a 
basic  slag  is  formed  by  charging  large  amounts  of  lime  into  the 
converter.  As  the  amount  of  lime  required  increases  with  the, 
amount  of  silicon  present,  for  economical  working,  the  silicon  in 
the  iron  must  be  kept  low,  and,  therefore,  cannot  furnish  the 
heat  necessary  for  the  conversion  of  the  metal  into  steel.  The 
phosphorus  is  converted  by  the  heat  into  its  oxide,  which  unites 
with  the  lime  of  the  slag  to  form  phosphate  of  lime.  The  heat 
from  the  combustion  of  the  phosphorus  provides  the  heat  for 
the  process.  The  percentage  of  this  element,  therefore,  may  be 
as  high  in  the  pig  as  it  is  possible  to  have  it,  without  unnecessarily 
prolonging  the  blow. 

The  phosphorus  cannot  be  eliminated  in  the  form  of  a  phos- 
phate in  the  acid  process,  because  iron  oxide  is  the  only  base 


148  IRON  AND   STEEL 

present  that  will  unite  with  the  phosphoric  acid  to  form  a  phos- 
phate; and  any  phosphate  of  iron  that  might  form  will  be  at 
once  broken  up  by  the  slag,  producing  sulphate  of  iron  and  leav- 
ing the  phosphoric  acid  unprotected.  This  acid  will  then  be 
reduced  by  the  manganese  and  carbon  of  the  bath  and  the 
recarburizers  and  the  phosphorus  will  return  to  the  bath. 

Although  the  basic  process  can  use  cheaper  pig  iron  than  the 
acid  process,  it  is  a  more  costly  method  because  of  the  amount  of 
lime  that  must  be  used  and  the  smaller  output  of  the  converter. 
It  is  also  generally  contended  that  the  steel  is  not  as  reliable 
nor  as  uniform  in  quality,  due,  in  all  probability,  to  the  difficulty 
of  knowing  exactly  when  the  process  is  completed.  Neverthe- 
lAcT~]tj^Jargfity  ^^d  m  Kurope  i'or  railc^  rofe^  shapes,  etc. 

Description  of  Basic  Process.  —  In  the  basic  process,  the 
blowing  is  divided  into  two  parts  known  as  the  "  fore-blow"  and 
the  "  after-blow ";  a  higher  blast  pressure  and  a  longer  time  are 
required  than  in  the  acid  process.  At  the  beginning  of  the  blow, 
as  fast  as  the  oxides  of  silicon  and  manganese  are  formed,  they 
unite  with  the  lime  to  form  a  double  silicate  of  lime,  manganese, 
and  iron.  As  the  lime  is  greatly  in  excess,  a  high  basic  slag 
capable  of  holding  the  phosphorus  in  solution  as  phosphate  of 
lime  is  formed  at  the  start.  When  the  silicon,  manganese,  and 
carbon  are  eliminated  and  the  flame  drops,  as  in  the  acid  proc- 
ess, the  blowing  is  continued  until  the  phosphorus  is  oxidized; 
this  is  not  removed  very  rapidly  as  long  as  carbon,  silicon,  and 
manganese  are  present,  owing  to  the  affinity  of  these  elements 
.for  oxygen  at  a  high  temperature  being  greater  than  the  affinity 
of  phosphorus.  The  combustion  of  the  phosphorus  produces  a 
great  deal  of  heat  and  the  iron  is  protected  from  oxidation  by 
the  phosphorus  as  long  as  very  much  of  it  is  present. 

When  charging  the  converter,  the  lime  is  placed  at  the  bot- 
tom and  the  molten  metal  is  poured  upon  it.  Sometimes  this 
lime  is  preheated;  at  other  times,  coke  or  coal  is  charged  with  it 
and  the  blast  is  turned  on  sufficiently  to  burn  the  fuel  and  heat 
the  lime.  During  the  first  part  of  the  blow,  the  metal  should 
be  as  hot  as  possible  so  as  to  prevent  slopping;  but  before  the 
steel  is  poured,  the  temperature  should  be  reduced.  During  the 


BESSEMER   PROCESS  149 

fore-blow,  the  conditions  of  the  charge  are  shown  by  the  flame 
and  the  temperature  is  regulated  by  varying  the  blast  or  by  the 
addition  of  scrap.  In  the  after-blow,  the  conditions  are  judged 
entirely  by  the  amount  of  air  blown  through  the  metal  and  no 
attention  is  paid  to  the  flame  or  other  indications.  This  period 
is  determined  by  experiment  for  different  percentages  of  phos- 
phorus, but  is  approximately  one-half  the  length  of  the  fore- 
blow. 

Basic  Pig  Iron.  —  In  the  basic  process,  the  pig  iron  used 
should  contain  from  2  to  3  per  cent  of  phosphorus,  less  thanjx^p 
per  cent  of  silicon,  from  0.75  to  3  per  cent  of  manganese,  and  not 
rnore_than  o.io  per  cent  of  sulphur.  In  fact,  when  very  jow_sul- 
phur  steel  is  to  be  made,  the  sulphur  in  the  pig  iron  should  not 
exceed  0.05  per  ce_nt1_  The  carbon  is  usually  from  3  to  3.50  per 
cent  and  is  in  the  combined  form.  The  manganese  in  most  cases 
ranges  from  i  to  2  per  cent  This  elemenTlurnishes  some  of 
the  hea±  at  the  beginning  of  the  blow,  as  the  low  silicon  content 
will  not  give  enough  heat  at  this  stage;  besides,  the  manganese 
has  the  tendency  to  desulphurize  the  metal,  which  is  a  great 
advantage,  as  the  basic  Bessemer  pig  iron  is  likely  to  be  high  m 
sulphur  because  of  the  low  silicon  content. 

Utilization  of  Slag.  —  The  large  amount  of  phosphoric  acid  in 
the  slag_^btamed  from  the  basic  process  makes  it  a  valuable 
fertilizer  and  it  is  largely  used  tor  this  purpose,  especially  in 
Germany^ For  this  purpose,  tnp_  slag  is  Aground  exceedingly 
fine  in  a  bell  mill  and  applied  in  this  form.  The  phosphate, 
However,  is  insoluble  so  tnat  only  a  part  oi  it  is  available  as  plant 
food.  When  the  pig  iron  is  not  high  enough  in  phosphorus,  the 
slag  is  returned  to  the  blast  furnace  and  resmelted.  In  this 
case,  the  high  percentage  of  lime  and  magnesia,  usually  from  55 
to  60  per  cent,  makes  it  valuable  as  a  flux;  besides,  the  iron  and 
manganese  it  contains  are  recovered.  The  more  economical 
method  of  disposing  of  the  slag  depends  entirely  upon  local  con- 
ditions, as  to  the  cost  of  the  flux  and  the  value  of  the  slag  as 
fertilizer. 

Mixers.  —  Converters  were  formerly  charged  with  metal  that 
had  been  melted  in  a  cupola.  In  order  to  avoid  the  cost  and 


IRON  AND   STEEL 


labor  of  this  remelting  of  the  pig  iron,  many  attempts  have  been 
made  to  use'  the  molten  blast-furnace  product.  The  steel  pro- 
duced, however,  varied  greatly  in  quality,  because  of  the  differ- 
ence in  the  various  charges.  This  trouble  is  eliminated  with  the 
use  of  a  mixer.  This  device  is  a  large  steel-plate  firebrick-lined 
structure.  The  metal  from  the  blast  furnace  is  poured  into  this 
and  held  until  wanted.  As  it  holds  from  150  to  200  tons,  it 
contains  the  metal  from  several  heats,  so  that  the  metal  for  the 


Fig.  5.     Pouring  Molten  Iron  from  Mixer  into  Ladles  for  Transpor- 
tation to  Open-hearth  Furnaces  or  Bessemer  Converters 

converters  or  open-hearth  furnaces  is  more  uniform  in  com- 
position. Besides  reducing  the  amount  of  metal  lost  in  the 
blast,  the  mixer  furnishes  the  metal  exactly  as  it  is  wanted  and 
in  the  proper  amount,  for  the  ladle  that  carries  the  metal  to 
the  converter  is  placed  upon  a  scale,  and  the  pouring  from  the 
mixer  is  stoppeoljwhen  the  required  weight  is  in  the  ladle.  Fig. 
5  shows  molten  iron  being  poured  from  a  mixer  into  ladles  for 


BESSEMER   PROCESS  151 

transportation  to  either  Bessemer  or  open-hearth  furnaces. 
Cupolas  are  usually  operated  in  connection  with  the  mixer  to 
supply  part  of  the  metal,  should  the  blast-furnace  output  fall 
below  the  converting  capacity. 

Physical  Characteristics  of  Bessemer  Steel.  —  The  Manufac- 
turers Standard  Specifications  for  Structural  Steel,  as  revised 
April  21,  1914,  cover  three  classes  of  steel:  Class  A,  which  is 
used  for  railway  bridges  and  ships;  Class  B,  which  is  used  for 
buildings,  highway  bridges,  crane  sheds,  and  similar  structures; 
and  Class  C,  which  is  used  for  structural  rivets.  Of  these,  only 
Class  B  may  be  made  by  the  Bessemer  process,  in  which  case  it 
is  specified  that  the  phosphorus  content  must  not  exceed  o.io 
per  cent.  The  specifications  for  physical  properties  require  for 
this  Bessemer  steel  a  tensile  strength  of  from  55,000  to  65,000 
pounds  per  square  inch;  a  maximum  yield-point  of  one-half  the 
tensile  strength;  and  a  minimum  percentage  of  elongation  in 
eight  inches  equal  to  1,400,000  -r-  tensile  strength.  The  elon- 
gation in  two  inches  should  be  a  minimum  of  22  per  cent.  The 
steel  may  have  a  tensile  strength  up  to  70,000  pounds  per  square 
inch,  provided  the  elongation  is  not  less  then  the  percentage 
required  for  a  steel  having  65,000  pounds  per  square  inch  tensile 
strength. 


CHAPTER  VIII 
OPEN-HEARTH   STEEL 

WHILE  the  Bessemer  process  makes  it  possible  to  produce  steel 
cheaply  in  large  quantities,  so  that  it  replaces  wrought  iron  for 
many  purposes,  the  process  can  be  used  for  making  steel  only 
from  pig  iron  made  from  certain  ores.  In  the  acid  Bessemer 
process,  only  pig  iron  with  a  low  phosphorus  content  can  be 
used,  while  in  the  basic_Eessemer  process,  the  phosphorus  content 
must  be  considerably  higher,  there  being  an  intermediate  stage" 
of  ore  and  pig  iron  which  has  too  much  phosphorus  for  tVip  qrjrl 
Bessemer  process  and  too  little  for  the  basic.  This  condition 
led  to  the  development  of  the  open-hearth  process  which  is  now 
commercially  the  most  important  of  the  steel-making  methods. 

General  Description  of  Open-hearth  Process.  —  In  the  open- 
hearth  process,  which  is  somewhat  similar  to  the  puddling  process 
for  producing  wrought  iron,  but  operated  on  a  much  larger  scale, 
the  impurities  are  removed  from  a  bath  of  pig  iron  held  on  the 
hearth  of  a  regenerative  furnace,  the  iron  being  exposed  to  the 
action  of  the  flame  from  the  fuel,  which  generally  consists  of  a 
mixture  of  producer  gas  and  air.  The  charge  which,  besides 
pig  iron,  consists  of  a  mixture  of  scrap  iron,  scrap  steel,  and  iron 
ore,  is  exposed  to  the  intense  heat  produced  by  the  fuel  for 
seven  or  eight  hours,  the  process  being  stopped  when  the  bath 
of  iron  has  the  right  proportions  of  carbon,  as  determined  by 
chemical  analysis.  The  steel  may  then  be  withdrawn  from  the 
furnace  and  either  poured  into  ingots  and  rolled  into  shape,  or 
cast  into  molds,  producing  steel  castings.  The  furnaces  generally 
have  a  capacity  of  from  40  to  50  tons  of  molten  metal.  Furnaces 
having  a  capacity  as  high  as  200  tons  have  been  made.  While 
in  the  Bessemer  process  only  pig  iron  can  be  used,  it  is  practic- 
able in  the  open-hearth  process  to  also  use  scrap  of  wrought  iron 
and  steel,  because  of  the  high  temperature  produced  in  the  fur- 

152 


OPEN-HEARTH  STEEL  153 

nace  by  the  burning  of  gas  which  is  preheated  to  a  temperature 
of  about  1000  degrees  F.  before  entering  the  combustion  cham- 
ber, by  passing  it  through  the  regenerative  chambers  of  the  fur- 
nace. The  open-hearth  process  produces  a  more  uniform  and 
reliable  steel  than  the  Bessemer  process,  and  the  latter  steel  has 
been  largely  replaced  for  more  important  purposes  by  the  open- 
hearth  steel.  (See  "  Tonnage  Produced  by  Bessemer  and 
Open-hearth  Processes,"  in  Chapter  VII.) 

Basic  and  Acid  Processes.  —  The  open-hearth  process  may 
be  either  acid  or  basic,  according  to  the  character  of  the  lining. 
The  basic  process  is  dephosphorizing,  burnt  lime  being  added 
to  the  charge  to  remove  the  phosphorus.  In  the  acid  process, 
no  lime  is  required,  but  the  metal  charged  must  be  low  in  phos- 
phorus. Except  for  this  difference,  and  with  the  exception  of 
the  lining  of  the  furnace,  both  the  acid  and  basic  processes  are 
practically  the  same.  In  the  basic  process,  the  furnace  lining  is 
neutral,  while  in  the  acid  process,  the  lining  is  siliceous.  The 
acid  process  is  the  faster  and  cheaper  process,  but  the  difference 
in  cost  is  offset  by  the  greater  cost  of  pig  iron  and  scrap  free 
enough  from  phosphorus;  consequently,  a  very  large  percentage 
of  the  open-hearth  steel  produced  in  the  United  States  is  basic. 
The  gross  tonnage  in  1916  was  29,616,658  tons  for  the  basic 
process  and  1,798,769  tons  for  the  acid  process,  according  to  the 
American  Iron  and  Steel  Institute.  Included  in  the  tonnage 
given  for  the  basic  open-hearth  process,  there  were  3,436,457 
tons  of  "  duplex  steel"  ingots  and  castings  which  were  made  from 
metal  partly  purified  in  Bessemer  converters  and  finally  purified 
in  basic  open-hearth  steel  furnaces. 

Development  of  Open-hearth  Process.  —  Sir  William  Siemens 
made  steel  in  an  open-hearth  furnace,  in  1862,  by  melting  iron 
ore  in  a  bath  of  pig  iron.  The  ore,  when  reduced  in  the  furnace, 
furnished  the  oxygen  necessary  for  oxidizing  the  carbon,  silicon, 
and  manganese  in  the  pig  iron.  The  same  method  had  been 
tried  by  Heath  in  about  1845,  but  he  did  hot  succeed,  because 
he  could  not  produce  sufficient  heat  to  carry  on  the  process. 
The  invention  of  the  regenerative  furnace  by  Siemens  in  1861 
made  it  possible  to  obtain  the  required  heat,  and,  in  1864,  the 


154  IRON  AND   STEEL 

French  steel-makers,  Messrs.  Martin,  patented  a  process  of 
making  steel  by  melting  pig  iron  and  scrap  in  a  furnace  heated 
by  the  Siemens  regenerative  method.  On  the  European  con- 
tinent, the  process  is  generally  now  known  as  the  "  Siemens- 
Martin  process"  or  simply  the  "Martin  process."  In  Great 
Britain,  it  is  known  either  as  the  "  Siemens-Martin"  or  the  "  open- 
hearth  process,"  the  last  name  being  the  most  generally  used. 
In  American  practice,  the  name  "open  hearth"  is  almost  ex- 
clusively used.  Both  the  pig  iron  and  ore  (the  Siemens)  and 
the  pig  iron  and  scrap  (the  Martin)  processes  are  combined  in 
general  American  practice. 

Comparison  of  Bessemer  and  Open-hearth  Processes.  —  The 
open-hearth  process  differs  from  the  Bessemer  in  that  steel  of 
any  percentage  of  carbon  can  be  made,  while  the  Bessemer  proc- 
egs  can  be  used  only  for  the  manufacture  of  medium  and  low- 
As  it  does  not  depend  upon  the  oxidation  of  the 


impurities  for  the  heat  necessary  for  its  working,  the  open-hearth 
process  can  utilize  pig  iron  and  scrap  of  a  wide  range  of  analysis; 
besides,  the  operations  are  under  greater  control  than  in  the 
Bessemer  converter;  there  is  less  danger  of  the  oxidation  of  the 
metal;  the  product  is  more  uniform  and  reliable;  the  yield  of 
ingots,  compared  with  the  amount  of  metal  charged,  is  higher; 
and  samples  for  both  physical  and  chemical  tests  can  be  taken 
while  working. 

Open-hearth  Furnaces.  —  There  is  practically  no  difference 
in  the  acid  and  basic  furnaces.  Either  may  be  stationary  or 
tilting,  but  in  each  case  the  furnace  consists  of  a  rectangular 
hearth  connected  at  the  ends  with  regenerative  chambers.  The 
capacity  of  these  furnaces  varies  from  5  to  15  tons,  for  special 
steels,  up  to  60  and  80  tons,  for  standard  grades.  In  a  furnace 
producing  50  tons  of  ingots  at  a  time,  the  hearth  is  33  feet  long 
and  14  feet  wide.  Owing  to  the  difficulty  of  handling  the  metal 
in  larger  furnaces,  those  from  50  to  60  tons  capacity  are  usually 
preferred.  With  larger  furnaces,  there  is  often  trouble  in  pour- 
ing; either  the  metal  must  be  too  hot  at  the  beginning  of  the 
pouring  to  make  good  steel  or,  if  at  the  proper  temperature  when 
first  poured,  it  will  be  too  cold  at  the  end  of  the  pouring;  be- 


OPEN-HEARTH  STEEL 


155 


sides,  the  ingots  will  require  reheating  before  they  can  be  put 
through  the  rolling  mills. 

It  is  of  great  importance  that  the  hearth  be  well  proportioned. 
It  should  be  long  enough  to  insure  complete  combustion  over 
the  hearth;  otherwise  some  of  the  gases  will  burn  in  the  ports 
and  upper  checkerwork.  For  economical  working,  it  has  been 


Machinery 


Fig.  i.     Sectional  View  of  Open-hearth  Furnace 

found  that  the  maximum  width  is  about  15  feet  and  the  length  is 
from  two  to  two  and  one-half  times  this  dimension.  It  should 
be  shallow  enough  to  promote  thorough  heating  and  reason- 
ably quick  working  of  the  bath,  yet  deep  enough  to  minimize 
the  oxidation  of  the  metal  and  thus  avoid  over-burning  and  a 
reduction  in  the  output.  For  these  reasons,  the  depth  is  usually 
from  15  to  20  inches. 

Description  of  Open-hearth  Furnace.  —  In  Fig.  i  is  shown 
a  section  of  an  open-hearth  furnace,  together  with  a  plan  view 


156  IRON  AND   STEEL 

in  section  of  the  regenerative  chambers  and  flues.  After  the 
furnace  is  charged,  the  gas  and  air  in  a  gas-fired  furnace  are 
turned  on.  The  gas  enters  the  flue  A,  passes  through  the  gas 
chamber  B  where  it  is  heated  as  it  passes  through  the  checker- 
work,  and  then  enters  the  furnace  through  the  ports  C.  At  the 
same  time,  air  from  flue  D  passes  through  the  flues  into  the  air 
chamber  E  and  then  through  port  F  into  furnace  G,  where  the 
combustion  takes  place.  The  waste  gases  then  pass  through  the 
ports  H  and  J  into  chambers  K  and  L,  which  are  heated  by  them 
before  they  pass  out  through  the  chimney  M .  When  chambers 
B  and  E  become  cooled,  dampers  N  and  P  are  shifted,  forcing 
the  gas  through  chamber  K  and  the  air  through  chamber  L. 
The  waste  gases  pass  to  chimney  M  through  chambers  B  and  E, 
which  are  now  heated.  In  this  way,  the  gas  and  air  are  always 
preheated  by  passing  through  the  chambers  that  have  previously 
been  heated  by  the  waste  gases,  and,  by  alternately  turning  on 
the  air  and  gas  from  the  left  or  the  right,  one  set  of  chambers  is 
constantly  being  heated;  hence,  the  air  and  gas  can  always  be 
preheated,  throughout  the  operation,  by  merely  making  use  of 
the  heat  in  the  exhaust  gases.  In  the  furnace  shown,  the  steel 
is  discharged  by  tilting  the  hearth  by  means  of  a  hydraulic  ram 
which  causes  the  furnace  to  rock  over  the  rollers  0. 

Making  the  Acid  Hearth.  —  The  entire  bottom  and  hearth 
are  built  on  and  supported  by  a  pan  of  heavy  riveted  steel  plates 
carried  by  beams  or  channels  resting  on  piers  entirely  inde- 
pendent of  the  rest  of  the  structure.  In  the  case  of  the  acid 
bottom,  this  pan  is  covered  with  two  or  three  layers  of  silica  or 
clay  brick,  preferably  the  former,  while  other  courses  are  stepped- 
up  at  the  ends  and  sides,  so  that  the  thickness  of  the  sand  bottom 
will  be  approximately  uniform  over  the  entire  hearth.  The 
furnace  is  then  gradually  brought  up  to  nearly  its  working  tem- 
perature, and  the  bottom  is  covered  with  a  thin  layer  of  sand. 
After  this  has  sintered,  more  sand  is  thrown  on,  in  thin  layers, 
sufficient  time  being  allowed  for  each  layer  to  set  perfectly. 
This  process  is  continued  until  the  hearth  is  from  1 6  to  24  inches 
thick  on  the  bottom  and  sides,  is  saucer-shaped,  and  the  sides 
are  carried  up  about  a  foot  above  what  is  the  level  of  the  metal 


OPEN-HEARTH  STEEL  157 

bath.  Sometimes,  the  bricks  are  covered  with  a  thin  layer  of 
sandstone  or  granite  chips,  which  are  softened  by  the  heat  and 
glaze  the  bricks.  The* completed  bottom  is  often  washed  down 
with  a  charge  of  open-hearth  slag. 

The  sand  should  be  silica  sand  with  just  enough  ferrous  oxide 
and  alumina  to  make  it  "set,"  or  partly  fuse,  at  the  full  heat  of 
the  furnace.  Owing  to  the  difficulty  of  obtaining  such  a  sand, 
a  common  practice  is  to  mix  a  pure  silica  sand  with  a  sand  that 
contains  a  larger  proportion  of  ferrous  oxide  and  alumina  than 
is  desired,  in  the  proportions  necessary  to  give  the  required 
mixture.  Quite  frequently  sands  of  different  fusing  points  are 
mixed  as  the  object  is  to  obtain  a  bottom  that  will  not  be  eroded 
by  the  iron  at  the  melting  temperature. 

Making  the  Basic  Hearth.  —  The  basic  hearth  is  made  by 
covering  the  pan  with  two  or  three  courses  of  clay  brick  and 
laying  upon  these  two  or  three  courses  of  magnesia  brick.  The 
sintered  sand  bottom  is  then  built  upon  this.  Sometimes  the 
magnesia  and  clay  bricks  are  separated  by  a  layer  or  two  of 
chrome  brick,  which  retards  the  "  breaking  out"  of  the  metal 
should  the  bottom  be  cut  through,  and  usually  allows  the  charge 
to  be  tapped  out  before  the  "break-out"  actually  occurs.  The 
complete  bottom  is  then  given  a  wash  heat  of  basic  slag  or  scrap, 
which  is  allowed  to  soak  into  the  bottom.  Sometimes  dolo- 
mite is  used  for  the  basic  hearth,  but  magnesite  is  preferred,  as 
it  makes  a  much  denser  bottom  and  one  that  can  be  relied  upon 
to  stay  in  place  when  once  set  and  soaked  full  of  slag,  while  dolo- 
mite bottoms  frequently  cut  through  and  come  up  in  patches. 

Open-hearth  Furnace  Walls.  —  The  end  walls,  known  as 
"blocks"  or  "bulkheads,"  of  the  open-hearth  furnace  are  from 
4  to  6  feet  thick,  because  they  contain  the  flues  or  passages  from 
the  regenerators.  These  walls  were  formerly  built  solid,  but  the 
present  practice  is  to  make  them  of  steel  frames  that  are  heavily 
faced  with  brick.  This  construction  has  been  found  to  be  the 
most  economical  to  maintain.  In  the  basic  furnace,  these  walls 
are  faced  with  magnesia  brick  up  to  the  ports.  In  the  acid 
furnace,  they  are  faced  with  silica  brick. 

The  side  walls  are  about  15  inches  thick.     In  the  acid  fur- 


158  IRON  AND   STEEL 

nace,  the  walls  are  built  of  silica  brick;  but  in  the  basic,  they  are 
made  of  magnesia  brick  up  to  a  few  courses  above  the  slag  line, 
above  which  point  they  are  made  of  silica  brick.  Sometimes 
one  or  more  courses  of  chrome  brick  are  placed  between  the 
silica  and  magnesia  brick  to  prevent  any  fluxing  action  between 
the  two,  should  the  temperature  rise  above  the  normal.  Some- 
times steel  or  iron  plates  are  placed  outside  the  front  and  back 
walls  of  the  furnace  to  strengthen  them.  This  construction  is 
objectionable,  however;  as  far  as  possible,  the  walls  should  be 
bare.  When  the  plating  is  used,  it  is  almost  impossible  to 
patch  the  walls  when  they  become  thin. 

Roof  of  Open-hearth  Furnace.  —  The  whole  structure  is  held 
together  by  heavy  beams,  called  "  bucks tays,"  set  perpendicu- 
larly along  the  sides  and  ends  and  connected  by  tie-rods  and 
turnbuckles.  This  arrangement  permits  the  quick  and  easy 
adjustment  of  these  parts  to  allow  for  contraction  and  expan- 
sion of  the  walls.  The  roof  is  supported  by  heavy  channels 
that  form  part  of  the  framework,  although  at  one  time  it  was 
permitted  to  rest  upon  the  walls.  This  latter  construction  was 
found  faulty,  because  the  walls  could  not  be  patched  without 
danger  of  damaging  the  roof;  besides,  the  weight  of  the  roof 
resting  on  the  walls  was  likely  to  distort  them,  and  at  times 
caused  the  walls  to  fall  when  they  were  partly  cut  through  by 
the  metal.  By  the  present  method,  the  walls  may  be  repaired 
or  renewed  without  disturbing  the  roof.  Quite  frequently,  the 
roofs  are  arched  from  port  to  port  as  well  as  across  the  furnace, 
which  insures  stability  of  construction  as  well  as  providing  for 
expansion. 

The  roof  is  invariably  built  of  silica  brick  and  should  be  suffi- 
ciently high  to  prevent  its  being  burnt  away  by  the  impinging 
flame  from  the  ports.  Its  thickness  varies  with  the  size  of  the 
furnace,  but  it  is  generally  from  8  to  13  inches.  In  the  earlier 
furnaces  the  roof  was  made  comparatively  low  in  order  to  keep 
the  flame  close  to  the  bath,  but  this  plan  has  been  abandoned 
because  of  the  excessive  repairs  made  necessary  by  the  rapid 
burning  away  of  the  roof  when  so  arranged.  Still,  the  distance 
from  the  hearth  to  the  roof  should  not  be  too  great;  sometimes 


OPEN-HEARTH   STEEL  159 

the  working  of  the  furnace  has  been  improved  by  reducing  this 
height. 

Ports  of  Open-hearth  Furnace.  —  The  successful  operation  of 
an  open-hearth  furnace  depends  largely  upon  the  construction 
of  its  ports,  which  is  the  name  given  the  openings  through  which 
the  air  and  gas  are  admitted.  These  ports  are  filled  alternately 
with  the  inflowing  gas  or  air  and  the  outflowing  gases  of  com- 
bustion, which  contain  incandescent  particles  of  ore,  limestone, 
slag,  etc.  They  are  generally  built  of  silica  brick.  They  may 
have  water-cooling  plates  placed  around  them,  but  paving  the 
port  with  magnesia  brick  or  fine  chrome  ore  and  daubing  the 
face  with  ore,  however,  seem  to  be  among  the  most  satisfactory 
preserving  methods.  The  position  and  pitch  of  the  ports  must 
be  carefully  planned.  They  are  connected  by  "up-takes"  with 
the  regenerative  chambers  and  are  so  arranged  that  the  air  and 
gas  mix  and  ignite  as  soon  as  they  pass  into  the  melting  chamber. 
The  air  is  placed  above  the  gas  and  thus  protects  the  roof  from 
the  intense  heat  generated,  while  the  gas  underneath  prevents 
the  air  from  directly  striking  the  charge  and  thus  causing  undue 
oxidation.  As  the  air  is  heavier  than  the  gas,  this  arrangement 
also  causes  the  flame  to  be  thrown  toward  the  bath  and  away 
from  the  roof. 

The  ports  are  usually  placed  so  that  the  gases  will  meet  from 
two  to  five  feet  above  the  bath.  If  they  meet  too  near  the  bath, 
the  combustion  will  be  incomplete,  because  the  gases  will  be 
cooled  by  the  bath.  If  they  meet  too  high  above  the  bath,  the 
most  intense  temperature  will  be  at  a  point  So  high  that  the  roof 
and  sides  will  be  damaged.  In  addition,  if  the  pitch  is  too  flat,  the 
flame  will  not  be  brought  down  sufficiently  on  the  metal  and  the 
combustion  will  be  too  high  in  the  melting  chamber  and  will 
distort  the  brickwork.  If  the  pitch  is  too  steep,  the  flame  will 
strike  the  bath  before  the  combustion  is  complete;  besides,  the 
heat  will  tend  to  concentrate  in  one  place  instead  of  being  evenly 
distributed  over  the  hearth.  In  most  large  furnaces,  there  is 
one  gas  and  one  air  port  at  each  end;  but  some  furnaces  have 
two  air  and  one  gas  port,  while  others  have  two  gas  and  two 
air  ports  at  each  end.  In  other  furnaces,  still  other  arrangements 
of  the  ports  are  made. 


160  IRON  AND   STEEL 

Regenerators.  —  The  gas  and  air  chambers,  or  regenerators, 
formerly  were  placed  directly  underneath  the  furnace;  but, 
owing  to  the  difficulty  of  making  repairs  and  of  keeping  the 
brickwork  gas-tight  and  air-tight,  and  the  delay  and  expense 
caused  should  the  metal  cut  into  the  checkerwork,  these  cham- 
bers are  now  separated  from  the  furnace.  Both  air  and  gas 
chambers  are  made  of  checkerwork  so  arranged  as  to  expose  a 
large  surface  to  the  gas.  At  one  time,  they  were  made  of  the 
same  size,  but  the  present  practice  is  to  make  the  air  chamber  one 
and  one-half  times  the  size  of  the  gas  chamber,  because  that  is 
the  proportion  in  which  the  air  and  gas  must  mix  for  their  proper 
combustion. 

The  gas  chambers  may  be  placed  on  either  side  of  the  air 
chambers  and  for  a  60- ton  furnace  should  be  from  13  to  18  feet 
high  and  have  a  capacity  of  90  cubic  feet  per  ton  of  steel.  Some- 
times the  bricks  are  laid  so  as  to  give  a  number  of  small  horizontal 
flues  in  the  chamber,  but  more  generally  they  are  staggered.  By 
this  plan,  the  waste  gases  are  brought  into  more  intimate  con- 
tact with  the  bricks,  assuring  a  better  absorption  of  heat  from 
the  waste  gases  and  more  thorough  reabsorption  of  this  heat 
by  the  unburned  gas  and  air  when  the  currents  are  reversed. 
The  openings  between  the"  bricks  and  the  exposed  ends  must  not 
be  so  large  that  the  surface  will  not  absorb  enough  heat  from 
the  waste  gases  nor  sufficiently  heat  the  gas  or  air  when  the 
current  is  reversed.  On  the  other  hand,  they  must  not  be  so 
small  that  the  openings  will  clog  rapidly  with  flue-dust.  In 
many  cases,  the  checkerwork  is  built  of  standard  g-inch  brick 
and  the  openings  are  approximately  3!  by  4  inches  wide. 

"  Slag  pockets"  should  be  placed  at  the  bottom  of  the  uptake. 
These  are  open  chambers  in  which  fine  particles  of  ore,  slag,  and 
limestone  settle  before  the  gases  enter  the  checkerwork.  This 
arrangement  reduce,s  the  tendency  of  the  small  openings  to  clog 
and  thus  improves  the  working  of  the  furnace.  Manholes  and 
clean-out  doors  permit  the  rapid  cleaning  of  these. 

In  many  instances  the  checkers  are  built  of  first  quality  clay 
brick,  although  in  some  plants  the  ten  or  twelve  top  courses 
are  made  of  silica  brick.  The  present  tendency,  however,  is  to 


OPEN-HEARTH  STEEL  161 

use  silica  brick  throughout,  or  to  build  the  five  or  six  top  courses 
of  magnesia  brick.  It  is  claimed  that  the  silica  bricks  clog  less 
rapidly  than  the  clay  and  do  not  take  on  a  carbon  coating  as 
quickly.  Silica  brick  also  expands,  thereby  holding  everything 
tightly  as  the  furnace  is  heated. 

Operation  of  Regenerators.  —  When  the  furnace  is  in  opera- 
tion, the  air  and  gas  enter  through  the  chambers  and  ports  in  one 
end  and  ignite  as  they  mix  in  the  melting  chamber.  The  waste 
gases  of  combustion  then  pass  through  the  ports  in  the  other  end 
and  passing  through  the  gas  and  air  chambers  enter  the  chimney. 
In  their  passage  through  the  flues  and  checkerwork,  the  waste 
gases  give  up  their  heat  and  pass  up  the  chimney  comparatively 
cool.  After  a  given  time,  usually  fifteen  or  twenty  minutes, 
the  valves  are  reversed  and  the  air  and  gas  pass  through  those 
chambers  that  have  just  been  heated  and  the  waste  gases  pass 
through  and  heat  the  chambers  through  which  the  air  and  gas 
have  just  passed.  With  each  reversal  of  the  gases,  the  tem- 
perature of  the  air  and  gas  is  raised  and  as  the  temperature  of 
the  bath  is  also  increased,  especially  toward  the  end  of  the  heat, 
unless  the  gas  and  air  are  carefully  regulated,  the  furnace  "  will 
melt  itself  down"  in  a  short  time. 

Oil  as  a  Fuel.  —  Open-hearth  furnaces  must  be  heated  by  a 
gaseous  fuel.  Oil  vaporized  by  steam  or  air  is  one  of  the  best 
fuels,  but  its  use  is  restricted  to  those  localities  where  oil  is 
plentiful  and  cheap.  Oil  requires  no  preheating  and  is  of  high 
calorific  value,  is  regular  in  quality,  and  permits  a  uniform  opera- 
tion of  the  furnace;  but  its  flame  is  short,  and  unless  care  is 
taken,  the  roof  will  be  cut  out  and  the  metal  of  the  bath  over- 
oxidized. 

Natural  Gas.  —  Natural  gas  is  considered  the  ideal  fuel.  It 
is  low  in  cost,  has  no  sulphur,  is  clean  and  convenient  to  use, 
requires  no  preheating,  has  a  high  calorific  value,  and  its  purity 
produces  a  pure  steel  or  allows  the  use  of  poor  raw  material. 
Its  use,  however,  is  restricted  to  those  regions  where  it  is  plentiful 
and  cheap;  although  it  has  been  piped  to  plants  two  hundred 
miles  from  its  source.  Natural  gas  is  a  mixture  of  methane  and 
other  hydrocarbon  gases  and  hydrogen.  It  is  found  principally 


1 62    *  IRON  AND   STEEL 

in  the  western  part  of  Pennsylvania  and  the  adjacent  parts  of 
Ohio  and  West  Virginia.  Its  pressure  at  the  wells,  which  vary 
in  depth  from  1000  to  4000  feet,  is  frequently  so  great  as  to 
render  the  gas  difficult  to  control,  but  in  the  lines  a  pressure  of 
from  six  to  ten  ounces  per  square  inch  is  maintained.  Its  calo- 
rific value  averages  from  970  to  1010  B.T.U.  per  cubic  foot. 

As  neither  oil  nor  natural  gas  requires  preheating,  regenerative 
chambers  are  used  for  the  heating  of  the  air  alone.  At  first  an 
effort  was  made  to  preheat  natural  gas,  but  it  was  found  that  the 
gas  was  reduced  to  hydrogen  or  lower  hydrocarbons  which  have 
less  heating  value  than  the  original  gas.  In  addition,  carbon  was 
deposited  in  the  chambers  in  the  form  of  a  hard  glassy  coke, 
the  heating  value  of  which  was  lost,  as  this  burned  on  the  re- 
versal of  the  furnace,  and  the  products  of  its  combustion  passed 
up  the  chimney  instead  of  into  the  furnace. 

Producer  Gas.  —  Owing  to  the  limited  areas  in  which  oil  and 
natural  gas  are  available,  artificial  gas  must  be  used  in  most 
open-hearth  furnaces.  While  any  artificial  gas  will  do,  theoreti- 
cally, producer  gas  is  the  one  used.  One  advantage  of  the  gas 
producer  is  that  inferior  kinds  of  fuel  may  be  utilized,  the  one 
essential  being  that  the  fuel  is  a  good  gas  coal  that  does  not 
contain  too  much  sulphur.  The  amount  of  tar  present  depends 
upon  the  coal.  While  the  tar  furnishes  from  6  to  12  per  cent  of 
the  calorific  value  of  the  gas,  some  of  the  tar  is  deposited  in  the 
gas  main,  valves,  and  flues,  and  so  is  not  burned  in  the  furnace. 
The  calorific  value  of  producer  gas  is  from  120  to  145  B.T.U. 
per  cubic  foot.  Producer  gas  is  generally  made  by  burning 
bituminous  coal  in  a  producer. 

Acid-furnace  Charge.  —  In  the  acid  process,  a  large  propor- 
tion of  the  charge  is  steel  or  wrought-iron  scrap  and  the  rest  is 
pig  iron  and  iron  ore.  The  quality  and  quantity  of  the  scrap 
and  the  analysis  of  the  pig  iron  determine  the  proportion  of 
each.  The  scrap  may  be  crop  ends  of  bolts,  rails,  structural 
sections,  machine-shop  turnings  and  borings,  etc. ;  but  as  neither 
sulphur  nor  phosphorus  is  eliminated  in  the  process,  the  charge 
must  contain  no  more  of  these  than  is  permissible  in  the  steel. 
In  order  to  indicate  the  relative  amounts  of  carbon,  the  pig  iron 


OPEN-HEARTH  STEEL  163 

is  frequently  referred  to  as  "hard  stock"  and  the  steel  and 
wrought-iron  scrap  as  "soft  scrap."  If  the  charge  contains  too 
much  scrap,  the  heat  will  be  so  low  in  manganese,  silicon,  and 
carbon  that  it  will  be  hard  to  work;  besides,  there  will  not  be 
enough  slag  formed  to  adequately  protect  the  bath  so  that  the 
oxidation  losses  will  be  high.  On  the  other  hand,  pig  iron  high 
in  silicon  with  a  small  proportion  of  scrap  will  give  the  bath 
such  a  heavy  slag  covering  that  it  cannot  be  penetrated  by  the 
heat.  Pig  iron  that  is  very  low  in  silicon  may  be  used  without 
other  additions. 

The  ore  used  is  a  red  hematite  that  is  as  free  as  possible  from 
all  impurities.  It  should  be  in  lumps  heavy  enough  to  sink 
through  the  slag  and  the  bath  of  metal,  so  as  to  reach  the  ele- 
ments it  is  to  oxidize.  It  should  contain  as  much  oxide  of  iron 
as  possible,  so  that  the  most  work  may  be  done  with  a  given 
weight  of  ore. 

Determining  Proportions  of  Charge.  —  In  general,  the  charge 
is  so  adjusted  that  when  melted  the  bath  contains  from  0.30 
to  0.60  per  cent  of  carbon  above  the  point  actually  required  in 
the  steel.  If  too  little  pig  iron  is  used,  all  the  carbon,  silicon, 
and  manganese  in  the  bath  will  be  oxidized  before  the  metal  is 
ready  to  tap.  As  a  result,  the  metal  will  become  pasty  and  oxide 
of  iron  will  be  rapidly  formed,  thus  wasting  the  metal  by  in- 
creasing the  melting  loss;  besides,  if  the  slag  is  not  acid  enough, 
the  ferrous  oxide  will  form  ferrous  silicate,  which  will  score  the 
bottom,  while  the  oxides  introduced  into  the  bath  will  be  diffi- 
cult to  remove  and  will  injure  the  steel,  making  it  "wild"  to 
handle  in  the  furnace  and  ladle.  The  remedy  for  too  little  pig 
iron  in  the  bath  or  a  heat  melting  "low"  or  "soft"  is  to  add  pig 
iron,  or  "pig  up,"  to  give  sufficient  carbon  and  silicon  to  bring 
the  bath  to  a  boil  and  obtain  the  necessary  temperature  to  tap 
the  heat.  This,  however,  causes  a  loss  of  time,  because  each 
addition  of  pig  iron  lowers  the  temperature  of  the  bath  and  re- 
quires more  pig  than  if  the  metal  were  added  in  the  first  place. 
If  too  much  pig  iron  is  charged,  no  harm  is  done  to  the  quality 
of  the  steel  as  the  bath  is  then  high  in  carbon  and  possibly  con- 
tains some  silicon  and  manganese.  These  can  be  "boiled  out" 


164 


IRON  AND   STEEL 


OPEN-HEARTH  STEEL  165 

but  the  usual  method  is  to  add  ore,  which  hastens  the  oxidation 
of  the  impurities. 

The  proportions  of  the  charge  are  fixed  by  a  study  of  the  re- 
actions that  occur.  The  silicon  and  manganese  are  deoxidized 
to  form,  with  the  manganese  and  iron  in  the  bath,  a  double  sili- 
cate of  manganese  and  iron,  which  rises  and  forms  the  slag;  the 
carbon  is  deoxidized  to  carbon  monoxide,  and  then  to  carbon 
dioxide,  in  which  form  it  passes  off. 

Method  of  Charging  the  Acid  Furnace.  —  In  the  acid  process, 
the  iron  is  charged  first,  generally  in  a  molten  condition  direct 
from  the  blast  furnace  (after  being  placed  temporarily  in  the 
mixer)  so  as  to  protect  the  hearth  from  the  oxide  of  iron  formed 
by  the  oxidation  of  the  scrap  by  the  flame.  Should  this  oxide 
come  into  contact  with  the  bottom  of  the  hearth,  it  will  form  a 
silicate  of  iron  which  will  rapidly  cut  the  bottom.  The  cutting, 
or  "  scorification, "  of  the  bottom  not  only  may  cause  a  hole  to  be 
cut  through  the  bottom  of  the  hearth,  but  the  sand  may  be  so 
impregnated  with  iron  that  its  refractory  power  and  ability  to 
withstand  the  action  of  the  metal  is  lessened.  One  of  the  open- 
hearth  furnaces  shown  in  Fig.  2  is  receiving  a  charge  of  molten 
iron  from  a  ladle. 

Sometimes,  when  charging  the  furnace  with  pig  iron  in  the 
form  of  bars,  only  a  part  of  the  pig  iron  is  placed  on  the  bottom 
of  the  hearth,  the  rest  being  placed  on  top  of  the  scrap.  Melters 
udng  this  plan  contend  that  the  pig  iron  on  top  of  the  scrap  will 
melt  first  and  its  carbon,  silicon,  and  manganese  will  protect  the 
iron  of  the  scrap  from  excessive  oxidation. 

The  charging  should  be  done,  if  possible,  at  one  time.  Some- 
times, however,  pig  iron  is  allowed  to  heat,  or  even  partly  melt, 
before  the  scrap  is  added.  It  is  claimed  that  by  this  practice 
the  stock  has  time  to  heat  up  as  added,  so  that  the  melting  goes 
on  much  faster.  Other  melters  contend  that  the  slow  charging 
cools  off  the  furnace,  because  the  doors  are  opened  so  long; 
besides,  the  oxidation  loss  is  greater  and  more  gas  is  used.  If 
a  furnace  is  properly  designed,  its  regenerative  capacity  should 
be  such  that  the  heat  in  the  checkerwork  will  prevent  the  fur- 
nace being  chilled  by  too  rapid  charging. 


1 66  IRON  AND   STEEL 

Charging  Machines.  —  Although  small  furnaces  are  charged 
by  hand,  machines  must  be  used  in  the  case  of  larger  ones.  These 
do  the  work  in  about  one-third  the  time  and  charge  more  con- 
tinuously, as  charging  is  the  hardest  and  hottest  part  of  the  fur- 
nace work.  The  machines  also  reduce  the  production  cost,  as 
one  machine  will  charge  five  or  six  furnaces,  each  of  which 
would  otherwise  require  at  least  three  or  four  men.  A  charging 
machine  consists  of  a  four-wheeled  truck  that  carries  a  heavy 
framework,  the  girders  of  which  extend  to  the  face  of  the  fur- 
nace. From  these  girders  is  suspended  a  carriage  that  carries 
and  operates  a  ram.  The  stock  for  charging  the  furnace  is 
placed  in  steel-plate  boxes.  One  end  may  be  made  of  cast  iron, 
but  the  end  that  is  fastened  to  the  ram  must  always  be  made  of 
cast  steel.  This  end  is  arranged  so  that  it  can  be  quickly  at- 
tached to  and  detached  from  the  ram,  and  the  sides  of  the  boxes 
are  slightly  flared  so  that  the  stock  will  readily  drop  out  when  the 
boxes  are  turned  over.  The  boxes  are  filled  in  the  stockyards 
and  placed,  in  sets  of  three  or  four,  upon  small  narrow-gage  cars 
that  run  just  in  front  of  the  furnace.  When  the  furnace  is  to  be 
charged,  the  cars  containing  the  boxes  are  run  into  position  and 
the  charging  machine  is  placed  directly  in  front  of  the  furnace 
door.  The  carriage  is  then  run  forward  until  the  ram  is  in 
position  for  attaching  one  of  the  stock  boxes  to  its  end.  As  soon 
as  this  is  attached,  the  ram  is  run  into  the  furnace  and  turned 
about  its  axis  until  all  the  stock  has  fallen  from  the  box,  when  the 
motion  is  reversed  and  the  ram  is  withdrawn.  As  soon  as  the 
empty  box  is  replaced  by  a  full  one,  the  ram  is  again  inserted  in 
the  furnace.  The  operation  of  lifting,  discharging,  and  replacing 
a  box  occupies  about  a  minute,  so  that  about  50  tons  of  material 
may  be  charged  into  a  furnace  in  about  an  hour.  At  one  time 
this  machine  was  operated  by  steam  or  compressed  air,  but  the 
present  machines  are  operated  by  electricity,  separate  motors 
being  employed  for  the  different  motions.  A  "high-type" 
open-hearth  charging  machine  made  by  the  Wellman-Seaver- 
Morgan  Co.,  Cleveland,  0.,  is  shown  in  Fig.  3. 

Operation  of  Acid  Furnace.  —  When  the  furnace  is  first  put 
into  operation,  the  flame,  as  a  rule,  is  kept  smoking  by  supply- 


OPEN-HEARTH   STEEL  167 

ing  less  air  than  is  necessary  for  the  complete  combustion  of  the 
gas.  This  plan  prevents  the  oxidation  of  the  scrap  at  the  be- 
ginning of  the  heat;  the  pig  iron  is  protected  from  oxidation  to  a 
large  extent  by  its  impurities.  Many  furnace  men,  however, 
favor  melting  as  quickly  as  possible,  even  if  the  oxidation  loss 
is  great.  In  the  operation  of  the  furnace,  the  aim  is  to  have  an 
even  flow  of  gas,  but  to  use  the  minimum  amount.  The  ideal 
flame  is  free  from  spots  and  flickering,  long  enough  to  heat  the 
whole  length  of  the  hearth.  If  the  flame  is  too  short  to  reach 
the  farther  end  of  the  furnace,  only  the  charge  at  one  end  of  the 


Fig.  3.     "High-type  "  Open-hearth  Charging  Machine 

hearth  is  heated,  and  that  is  badly  oxidized;  if  the  flame  is  so 
long  as  to  be  still  burning  as  it  enters  its  farther  port,  considerable 
gas  will  be  wasted.  The  proper  flame  will  melt  the  stock  rapidly 
and  uniformly.  A  swift  short  flame  dragged  along  by  the  draft 
of  a  wide-open  stack  damper  and  fed  with  too  much  air  will 
" glaze"  the  stock  so  that  it  will  melt  chiefly  at  the  top  of  the  pile. 
Such  melting  delays  oxidation  of  the  metal,  wastes  iron,  and 
makes  the  steel  "wild"  from  an  excess  of  dissolved  oxide. 

In  American  practice,  the  charge  is  usually  so  proportioned 
that  the  silicon  and  manganese  are  oxidized  when  the  charge  is 


1 68  IRON  AND   STEEL 

melted.  Generally  only  about  one- third  of  the  carbon  is  oxi- 
dized at  this  time,  because  its  affinity  for  oxygen  is  not  as  great 
as  that  of  the  other  elements.  If  the  silicon  and  manganese  in 
the  charge  are  low,  more  of  the  carbon  will  be  oxidized.  In  a 
normal  heat  for  soft  steel,  manganese,  silicon,  and  carbon  are 
eliminated  in  the  order  in  which  they  are  named  and  in  accord- 
ance with  their  affinity  for  oxygen.  When  the  charge  is  melted, 
the  bath  is  well  stirred  with  a  bar  or  " rabble"  and  the  height  to 
which  the  slag  boils  over  the  bar  as  it  is  moved  about  is  noted. 
The  colder  and  softer  the  metal,  the  higher  will  be  this  boil. 
The  boiling  produced  by  this  "rabbling"  frees  the  steel  from 
oxides. 

When  the  silicon  and  manganese  have  been  almost  entirely 
removed  and  the  carbon  has  been  brought  down  to  about  0.60 
per  cent,  the  ore  is  added  to  the  bath.  The  amount  that  may  be 
added  at  one  time  depends  upon  the  condition  of  the  bath.  If 
the  slag  is  cold,  the  addition  of  the  ore  chills  the  bath,  while  hot 
slag  permits  the  ore  to  be  added  quite  rapidly;  yet  care  must 
be  taken  that  the  ore  is  not  added  so  rapidly  as  to  cause  the 
bath  to  boil  over.  The  boiling  increases  in  violence  quite  slowly 
until  a  certain  point  is  reached,  after  which  the  addition  of  one 
or  two  lumps  of  ore  will  cause  the  whole  bath  to  boil  so  violently 
that  the  slag  and  metal  will  run  out  of  the  door.  At  the  same 
time  a  great  amount  of  carbon  monoxide  will  be  suddenly  evolved 
and  in  burning  to  carbon  dioxide  will  so  fill  the  furnace  with 
gas  that  the  flames  will  pour  from  all  openings.  As  soon  as 
enough  ore  is  charged  to  bring  the  carbon  content  to  the  desired 
point,  the  bath  should  be  allowed  to  become  quiet  before  it  is 
tapped. 

Should  too  much  ore  be  added  to  the  bath,  the  metal  may  be- 
come practically  carbonless  before  it  has  had  time  to  become 
hot;  to  prevent  its  freezing,  pig  iron  or  ferrosilicon  must  be 
thrown  in.  Ferrosilicon  is  used  when  the  bath  is  hot,  but  losing- 
its  carbon  too  rapidly;  pig  iron  is  used  when  the  bath  must  be 
heated  without  the  elimination  of  more  carbon. 

Recarburizing  the  Metal.  —  It  is  possible  to  calculate  the 
proportions  of  a  charge  so  accurately  that  the  amount  of  ore 


OPEN-HEARTH  STEEL  169 

necessary  to  oxidize  the  impurities  is  easily  determined.  The 
working  conditions,  however,  vary  so  much  that  the  steel  ob- 
tained by  this  method  would  not  generally  be  uniform  nor  of 
the  desired  quality;  therefore,  it  is  customary  to  oxidize  the 
bath  to  a  certain  point  and  then  raise  the  carbon  content  by 
recarburization.  The  addition  may  be  made  to  the  metal  in 
the  hearth  just  before  it  is  tapped  or  as  it  is  being  run  out  into 
the  ladle.  Any  manganese  or  silicon  that  the  steel  is  to  contain 
must  be  added  at  this  time,  if  all  manganese  and  silicon  that 
were  in  the  charge  were  removed  by  oxidation. 

The  recarburizer  most  generally  used  in  the  acid  open-hearth 
process  is  ferromanganese.  This  supplies  the  manganese  de- 
sired, reduces  the  oxide  of  iron  remaining  in  the  bath,  and  re- 
moves the  free  oxygen  held  in  the  gaseous  form.  It  mixes  better 
when  added  to  the  metal  in  the  furnace,  but  there  is  said  to  be 
a  greater  loss  of  the  manganese  than  when  added  in  the  ladle. 
When  the  heats  are  small,  or  high  manganese  or  silicon  steel  is 
being  made,  the  ferromanganese  is  heated  to  redness  before  it  is 
added  to  the  molten  metal;  for  medium  and  large-sized  heats, 
however,  the  recarburizer  is  not  usually  heated,  but  is  thrown 
into  the  ladle  so  as  to  mix  with  the  stream  of  the  metal. 

Spiegeleisen,  ferrosilicon,  silico-spiegel,  or  silicon  carbide, 
pig  iron,  and  powdered  coal  and  coke  are  also  used,  especially 
for  high-carbon  and  special  steels.  Aluminum  is  sometimes 
added  to  the  metal  when  it  is  in  the  ladle  or  after  it  has  been 
poured  into  the  ingot  mold  in  order  to  deoxidize  or  neutralize 
the  metal  and  thus  minimize  the  formation  of  blow-holes. 
Aluminum,  however,  has  a  tendency  to  increase  the  size  of  the 
pipe  or  shrinkage  cavity  in  the  ingot,  as  it  localizes  the  shrinkage. 

Testing  the  Metal.  —  The  successful  operation  of  an  open- 
hearth  furnace  requires  that  tests  be  made  at  regular  intervals 
to  determine  the  condition  of  the  metal  and  that  the  proper 
temperature  be  maintained.  As  no  apparatus  is  used  for 
measuring  the  temperature,  the  melter  must  become  skilled  in 
determining  the  temperature  of  the  melting  chamber  by  the  ap- 
pearance of  the  roof  and  side  walls  and  the  flame  and  slag,  as  he 
observes  these  through  the  blue  glass  in  the  peep  holes.  The 


170  IRON  AND   STEEL 

temperature  of  the  bath  is  determined  by  the  action  of  the  bath 
on  a  metal  rod.  If  the  bath  is  hot,  the  end  of  a  bar  used  to  stir 
the  bath  will  be  melted  off  quite  square;  if  the  bath  is  cold,  the 
end  of  the  rod  will  be  tapered.  The  rod  must  be  thrust  quickly 
through  the  slag  or  it  will  be  coated  with  slag  and  protected  from 
the  action  of  the  bath  and  thus  give  misleading  indications. 
The  "feel"  of  the  bath  as  the  bar  is  stirred  in  it  also  shows  the 


Fig.  4.  Seventy-five-ton  Ladles  placed  at  Open-hearth  Furnaces 
to  Receive  the  "Heat"  of  Molten  Steel  — Homestead  Works  of 
Carnegie  Steel  Co. 

condition;   sometimes  the  surface  is  of  the  proper  temperature 
while  the  bottom  contains  partly  melted  stock. 

A  common  custom  is  to  dip  up  with  a  test  spoon  some  of  the 
metal  from  the  bottom  of  the  bath  as  soon  as  all  the  stock  is 
melted.  This  metal  is'  at  once  poured  into  a  small  test  mold. 
The  melter  then  estimates  the  amount  of  carbon  in  the  bath 
and  the  amount  of  ore  required  to  reduce  the  carbon  to  the 
desired  point  by  the  fracture  of  the  test  piece.  Any  metal  that 
may  be  left  on  the  spoon  when  the  mold  is  filled  is  slowly  poured 
off  so  that  its  temperature  may  be  judged.  If  the  metal  pours 


OPEN-HEARTH   STEEL 


171 


off  clean  to  the  last  drop,  it  is  very  hot;  the  more  it  tends  to 
cling  to  the  spoon  the  colder  it  is.  A  little  of  the  slag  that  adheres 
to  the  handle  of  the  spoon  is  saved  from  each  heat.  These  sam- 
ples show,  by  the  changes  in  the  color,  the  progress  in  the  elimi- 
nation of  the  iron  oxide.  When  the  melter  thinks  that  enough 
ore  has  been  added  to  the  bath,  he  makes  another  test  and  in  one- 
half  hour,  a  third.  An  experienced  melter  can  usually  determine 
the  carbon  as  shown  by  the  fracture  within  two  or  three  hun- 
dred ths  of  a  per  cent,  in  samples  containing  less  than  0.20  per 


Fig.  5.     Casting  Crew  on  Open-hearth  Pouring  Platform  filling  Molds 
with  Molten  Steel  tapped  through  Bottom  of  Ladle 

cent  of  carbon.  Above  this  point,  there  is  a  greater  liability  to 
error,  which  increases  as  the  carbon  increases.  The  character 
and  temperature  of  the  metal  are  also  shown  by  the  way  it  pours, 
its  fluidity,  and  the  sparks  given  off.  The  test  pieces  also  show 
the  contraction  of  the  steel  on  cooling. 

Making  the  Ingots.  —  When  the  steel  is  ready,  the  molten 
metal  is  drawn  into  a  ladle  and  poured  into  the  molds.  (See 
Fig.  4.)  These  ladles  are  usually  made  of  heavy  riveted  steel 
plate  lined  with  two  courses  of  firebrick,  and  hold  from  30  to 


172 


IRON  AND   STEEL 


75  tons  of  metal.  They  are  carried  by  cranes  and  the  metal  is 
poured  from  them  through  the  bottom  as  shown  in  Fig.  5.  By 
this  plan,  the  metal  is  kept  under  better  control  than  when  the 
metal  is  poured  over  the  lip,  and  the  slag  is  prevented  from  pass- 
ing into  the  molds.  Sometimes  the  molds  are  placed  in  rows  in 
the  charging  pit;  but  more  commonly  they  are  placed  on  cars, 
which  are  then  run  directly  into  the  rolling  mill.  Fig.  6  illus- 
trates how  test  samples  are  obtained  at  the  open-hearth  pouring 
platform. 

In  ordinary  practice,  the  slag  is  held  in  the  furnace  until  all 
the  heat  is  tapped,  when  it  runs  out  and  forms  a  covering  for  the 
metal  in  the  ladle,  thus  protecting  it  from  loss  of  heat.  Some- 
times part  of  the  slag  is  run  off  into  a  slag  hole  under  the  tap 
hole. 

Basic  Furnace  Charge.  —  The  charge  of  the  basic  furnace 
differs  from  the  charge  of  the  acid  furnace  in  that  it  contains 
lime,  as  phosphorus  and  sulphur  are  to  be  removed  or  reduced. 
Because  of  the  irregularity  in  the  elimination  of  sulphur,  some 
mills  will  allow  no  more  sulphur  in  the  charge  than  is  permissible 
in  the  ingot.  Because  of  the  difficulty  of  removing  it,  the  sul- 
phur in  the  pig  iron  and  scrap  should  be  as  low  as  possible,  and 
never  over  0.05  per  cent  in  the  pig. 

The  lime  may  be  charged  in  the  form  of  limestone,  or  cal- 
cined oxide  commonly  known  as  "lime."  When  the  limestone 
is  charged,  as  is  the  common  practice,  and  is  calcined  on  the 
open-hearth,  the  resulting  liberation  of  carbon  dioxide  makes 
the  bath  boil  and  insures  a  lively  reduction  and  mingling  of  the 
elements;  but  the  heat  required  for  this  calcination  of  the 
limestone  appreciably  retards  the  operation  of  the  furnace. 
Besides,  there  is  a  greater  tendency  for  the  slag  to  boil  and  the 
metal  to  escape  in  the  form  of  gas.  Sufficient  lime  must  be 
charged  so  that  the  slag  will  be  basic  enough  to  supply  a  base 
with  which  phosphorus  can  combine  and  form  a  stable  compound. 
While  the  phosphorus  can  unite  with  the  iron  oxide,  the  same  as 
with  the  calcium  oxide,  the  iron  oxide  will  be  again  reduced  and 
the  phosphorus  will  be  returned  to  the  bath.  The  limestone  must 
be  as  pure  as  possible,  for  whatever  silica  it  may  possess  must 


OPEN-HEARTH  STEEL 


173 


first  be  satisfied  by  the  lime,  before  the  lime  is  available  for  the 
oxidation  of  the  bath.  In  order  that  the  amount  of  lime  may  be 
kept  down  as  much  as  possible  and  the  amount  of  slag  kept  low, 
the  pig  iron  charged  should  not  contain  more  than  one  per  cent 
of  silicon. 

Method  of  Charging  the  Basic  Furnace.  —  In  the  basic  proc- 
ess, the  hearth  is  generally  covered  by  the  limestone  before  the 


Fig.  6.     Obtaining  a  Sample  at  the  Pouring  Platform 

pig  iron  and  the  scrap  are  charged;  the  charge,  however,  may 
consist  entirely  of  molten  iron  directly  from  the  blast  furnace. 
Sometimes  only  part  of  the  limestone  is  charged  at  first  and  the 
rest  is  added  in  small  quantities  as  the  heat  proceeds,  while  the 
order  of  charging  the  pig  iron  and  scrap  may  also  be  reversed. 
The  chief  advantage  of  charging  all  the  limestone  first  is  that  it 


174  IRON  AND   STEEL 

affords  more  protection  to  the  bottom  of  the  bath  and  that,  as 
the  stone  is  decomposed,  the  carbon  dioxides  and  calcium  oxide 
pass  through  the  pasty  mass  and  thus  help  the  action  of  the 
bath.  The  objection  to  this  practice  is  that  the  lime  sometimes 
sticks  to  the  bottom  of  the  hearth,  thus  reducing  the  melting 
space.  This  can  be  avoided  with  a  little  care. 

When  molten  pig  iron  is  used,  the  scrap  is  placed  upon  the 
limestone  and  the  molten  iron  is  poured  from  a  ladle  on  top  of  it. 
The  advantage  of  using  hot  metal  is  that  less  time  is  required 
for  the  heat,  thus  increasing  the  output  of  the  furnace;  besides, 
the  time  and  labor  of  making  the  pigs  are  avoided.  Usually 
the  molten  metal  is  not  poured  into  the  furnace  until  the  scrap 
has  been  heated  enough  for  it  to  begin  to  "drip." 

Operation  of  Basic  Furnace.  —  In  order  to  eliminate  the  phos- 
phorus and  sulphur,  it  is  essential  that  a  basic  slag  be  formed  from 
the  start.  The  slag  produced  when  the  heat  is  melted  (unless  it 
is  very  hot)  is  sluggish,  basic,  and  contains  lumps  of  limestone; 
but,  as  a  rule,  the  phosphorus  is  largely  eliminated.  Usually  a 
test  of  the  bath  is  taken  at  this  time  to  determine  the  amount 
of  ore  that  must  be  added  to  produce  the  steel  desired,  and  also 
to  determine  the  phosphorus  content.  If  the  test  piece  is  too 
high  in  phosphorus,  its  fracture  will  show  a  crystalline  formation 
known  as  the  "phosphorus  cross."  As  soon  as  all  the  slag  is 
melted,  sufficient  ore  must  be  added  to  oxidize  the  carbon  and 
produce  a  vigorous  boiling;  but  as  the  carbon  approaches  the 
desired  point,  lime  is  added  to  keep  the  slag  basic  so  as  to  pro- 
mote the  elimination  of  the  phosphorus.  The  progress  of  this 
elimination  should  be  watched  closely,  as  often  it  is  sufficiently 
advanced  at  the  time  the  carbon  is  low  enough  and  the  heat  is 
hot  enough  to  tap.  As  in  the  acid  process,  the  ore  should  be 
introduced  early  and  allowed  to  work  until  its  iron  oxide  has 
been  used,  as  far  as  possible,  in  eliminating  the  silicon,  man- 
ganese, and  carbon  from  the  bath.  The  best  metal  is  produced 
by  working  heats  for  some  time  after  the  effects  of  the  ore  are 
worn  off,  to  reduce  the  iron  oxide  in  the  slag  and  steel. 

Elimination  of  Phosphorus  and  Sulphur.  —  The  phosphorus 
is  oxidized  by  the  flame  and  ore  to  phosphoric  acid,  which  in  the 


OPEN-HEARTH  STEEL  175 

presence  of  the  lime  unites  to  form  a  phosphate  of  lime.  This 
phosphate  is  practically  stable  under  normal  conditions,  although 
if  the  proper  precautions  are  not  observed,  part  of  the  phosphorus 
may  return  to  the  bath.  While  the  removal  of  the  phosphorus 
may  be  complete  before  all  the  carbon  is  burned,  most  of  the 
manganese  and  all  of  the  silicon  will  be  oxidized  before  desul- 
phurization  can  be  finished.  The  phosphorus  exists  in  the  slag 
as  a  phosphate  of  iron  and  calcium.  The  thermal  conditions 
accompanying  oxidation  of  phosphorus  favor  its  removal  during 
melting,  as  it  enters  the  slag  at  a  comparatively  low  temperature. 
In  good  basic  practice,  the  phosphorus  is  reduced  to  less  than 
0.04  per  cent  in  the  finished  steel  and  not  infrequently,  in  regular 
practice,  basic  steel  contains  but  from  o.oi  to  0.02  per  cent  of 
phosphorus. 

Sulphur  is  a  most  difficult  element  to  remove,  and  the  results 
obtained  when  efforts  are  made  to  remove  it  are  irregular  and 
uncertain.  In  good  basic  practice,  about  one-third  of  the  sul- 
phur in  the  charge  is  usually  removed,  although  when  manganese 
and  lime  are  added  for  this  purpose,  from  50  to  70  per  cent  of 
the  sulphur  in  the  charge  may  be  removed. 

In  the  Sautter  process,  oxy-chloride  of  lime  is  used.  The 
process  requires  the  use  of  an  exceedingly  basic  slag  before  the 
oxy-chloride  is  added,  as  it  is  claimed  that  it  is  this  excessive 
basicity  with  the  fluidity  due  to  the  oxy-chloride  of  lime  that 
enables  the  slag  to  absorb  a  larger  amount  of  sulphur. 

Adding  the  Recarburizers.  —  In  the  basic  process,  the  recar- 
burizers  are  added  mostly  in  the  ladle.  If  manganese  is  added  to 
the  bath  in  the  furnace,  it  will  come  into  contact  with  the  slag 
and  reduce  some  of  the  calcium  phosphate,  thus  rephosphorizing 
the  steel;  in  addition,  much  of  the  manganese  would  be  lost 
through  oxidation.  In  some  plants  that  make  very  high-grade 
steel,  however,  large  lumps  of  manganese  are  thrown  into  the 
bath,  care  being  taken  that  the  pieces  are  so  heavy  that  they 
pass  right  through  the  slag  into  the  bath.  The  manganese  added 
in  this  manner  greatly  improves  the  quality  of  the  steel  by 
eliminating  the  oxides  from  the  bath.  It  is  not  uncommon  in 
the  decarburized  basic  metal  to  have  a  high  manganese  content 


176  IRON  AND   STEEL 

either  from  the  ore  added  to  the  bath  or  from  the  stock;  this 
fact  must  be  taken  into  consideration  when  recarburization  is 
being  made.  Carbon  recarburizers  must  always  be  added  in  the 
ladle,  because  if  the  carbon  comes  into  contact  with  the  slag, 
some  of  the  phosphorus  may  return  to  the  bath. 

Basic-hearth  Slag.  —  In  the  basic  hearth,  the  slag  must  not 
only  transmit  heat  and  oxygen  to  the  bath  and  protect  the  metal 
from  oxidation,  as  in  the  acid  furnace,  but  it  must  aid  in  the 
removal  of  the  phosphorus  and  sulphur.  For  these  reasons, 
more  attention  must  be  paid  to  this  part  of  the  bath  than  in  the 
acid  process.  It  is  essential  that  the  slag  is  basic  both  to  remove 
the  phosphorus  and  sulphur  and  to  preserve  the  lining  of  the 
hearth.  In  addition,  the  slag  must  be  fluid  in  order  that  it  may 
flow  freely  in  the  furnace  with,  or  immediately  after,  the  steel, 
and  that  the  reactions  may  take  place  easily.  The  lack  of 
fluidity  may  check  the  oxidation  of  the  metalloids  by  forming 
too  great  a  restriction  to  the  boiling. 

Should  the  slag  be  very  thin,  watery,  and  black,  burnt  lime 
or  limestone  must  be  added,  as  the  slag  contains  an  excess  of 
silica  and  iron  oxide.  With  such  a  slag,  the  dephosphorizing 
has  not  been  completed.  As  a  rule,  no  more  slag  than  is  ab- 
solutely required  must  be  formed,  as  it  is  a  waste  product.  It 
usually  ranges  from  8  to  20  per  cent  of  the  charge. 

Tilting  Furnaces.  —  Because  of  the  difficulty  of  tapping 
large  furnaces,  the  tilting  furnace  has  been  designed.  Two 
types  are  in  common  use:  One  rotates  on  its  axis,  while  the 
other  is  carried  by  a  crane  to  the  ladle  or  mold  into  which  the 
metal  is  to  be  poured.  In  each  case,  the  tap  hole  is  located 
above  the  metal  and  slag  line,  so  that  a  light  tamping  is  sufficient; 
besides,  all  metal  and  slag  are  drawn  off  so  that  the  bottom  lasts 
longer  and  the  back  wall  is  easily  patched.  The  acid  furnace  is 
lined  with  silica  brick  both  on  the  sides  and  the  roof.  The  basic 
hearth  is  lined  with  magnesite  brick,  which  is  carried  far  enough 
up  the  back  wall  so  that  the  slag  will  not  be  in  contact  with  the 
silica  brick  when  the  furnace  charge  is  being  poured.  The  use  of 
these  furnaces  is  especially  advantageous  in  the  basic  process,  as 
it  is  then  possible  to  remove  some  of  the  slag  and  thus  prevent 


OPEN-HEARTH  STEEL  177 

any  phosphoric  acid  that  has  passed  into  the  slag  from  returning 
to  the  metal.  Other  advantages  of  the  tilting  furnace  are: 
Cold  air  is  not  admitted  to  the  ports  when  the  gas  is  shut  off, 
because  the  port  connections  are  broken;  holes  in  the  bottom 
are  easily  repaired;  the  furnace  is  easily  tapped;  and  partly 
reduced  metal  is  easily  transferred  from  one  furnace  to  another. 

Most  tilting  furnaces  are  of  the  Talbot  type,  which  are  not 
removable  but  are  rotated  on  their  axes  by  hydraulic  rams  that 
cause  them  to  move  on  rocker-like  supports  until  the  metal  runs 
through  the  tap  holes.  These  furnaces  are  strongly  framed  steel 
casings,  approximately  rectangular  in  section,  inside  of  which 
a  brick  lining  is  built  up.  The  curved  rockers  on  their  underside 
roll  upon,  and  are  supported  by,  strong  steel  braces.  In  case  of 
accident,  the  furnace  always  returns  by  its  own  weight  to  its 
lev  si  position.  The  gas  and  air  openings  are  enclosed  in  a  cast- 
iron  water-cooled  ring  which  fits  into  a  corresponding  ring  in  the 
port  when  the  furnace  is  upright.  The  ports  are  built  inside  a 
strongly  framed  steel  structure  that  is  mounted  on  four  wheels. 
When  the  furnace  is  to  be  poured,  each  port  is  drawn  back  to 
avoid  any  friction  between  the  ports  and  the  furnace  ends.  The 
ends  of  the  uptake  from  the  regenerators  are  closed  with  cast- 
iron  water  troughs  into  which  rings  on  the  underside  of  the  port 
openings  project. 

One  of  the  special  features  of  the  tilting  furnace  is  the  ''fore- 
hearth"  which  allows  the  steel  to  be  poured  directly  into  the 
molds  without  the  use  of  a  ladle.  This  forehearth  is  a  brick- 
lined  box-shaped  casting  that  is  provided  with  two  pouring  holes 
and  stoppers.  These  holes  are  spaced  the  proper  distance  apart, 
so  that,  when  the  furnace  is  tilted,  the  metal  flows  into  the 
hearth  and  then  into  both  of  the  molds,  which  are  carried  by  a 
small  car,  or  "  bogie. "  If  it  should  be  desired  at  any  time,  the 
forehearth  may  be  removed  and  a  spout  substituted  so  that  the 
steel  may  be  run  into  a  ladle  as  in  ordinary  practice. 

Talbot  Continuous  Process.  —  In  an  effort  to  increase  the 
output  of  the  open-hearth  furnace,  special  processes  have  been 
devised.  The  most  important  of  these  is  that  patented  by 
Benjamin  Talbot,  in  1899.  This  process  utilizes  the  tilting 


178  IRON  AND   STEEL 

furnace  and  is  based  upon  the  powerful  oxidizing  action  of  a  slag 
rich  in  iron  oxides.  It  consists  in  maintaining  in  the  furnace  a 
reservoir  of  metal  by  adding  to  the  bath  as  much  lime  and  pig 
iron  as  molten  steel  is  withdrawn.  Its  chief  advantages  are: 
A  larger  output  is  obtained;  the  process  is  worked  with  pig  iron 
and  oxides  or  ores,  so  that  the  use  of  scrap  is  unnecessary;  a 
greater  yield  is  obtained  from  the  metal  charged;  and  pig  iron 
high  in  silicon  and  phosphorus  can  be  used.  The  increased  yield 
of  steel  comes  from  the  iron  reduced  from  the  oxides  entering 
the  bath.  These  oxides  are  rolled  scrap,  mill  cinder,  and  ore. 
In  order  that  the  excess  of  slag  formed  may  be  removed,  a  hole 
is  placed  on  the  side  of  the  furnace  opposite  to  that  on  which 
the  steel  is  tapped,  and  the  furnace  is  arranged  to  tilt  in  this 
direction  until  the  slag  will  run  out.  Large  furnaces  are  used, 
hearths  holding  over  200  tons  of  metal  not  being  uncommon. 

At  the  beginning  of  each  week,  the  furnace  is  charged  and 
operated  in  the  usual  manner  for  open-hearth  work.  When  the 
heat  is  completed,  only  from  one-fourth  to  one-third  of  the  bath 
is  drawn  off  by  tilting  the  furnace  forward;  this  metal  is  recar- 
burized  in  the  ladle.  The  oxide  of  iron  is  then  added  to  the  bath 
and,  after  this  is  melted,  as  much  hot  metal  and  limestone  is 
poured  in  as  steel  was  tapped.  A  vigorous  boiling  action,  like  the 
Bessemer  blowing,  is  at  once  caused  by  the  discharge  of  large 
quantities  of  carbon  monoxide.  This  gas  burns  with  an  in- 
tensely hot  flame  and  generates  sufficient  heat  to  raise  the  tem- 
perature in  the  bath  so  that  the  producer  gas  is  shut  off  from  the 
furnace  at  this  time.  Within  a  few  minutes,  the  slag  is  dissolved 
of  its  iron  oxide  so  that  a  part  of  it  is  poured  off;  the  bath  is  then 
reduced  to  steel  of  the  desired  quality  by  adding  iron  ore  and 
lime.  As  soon  as  the  steel  is  produced,  a  part  of  the  bath  is 
again  poured  off  and  the  additions  made  as  before.  Sometimes 
the  methods  of  adding  the  oxides,  iron,  and  lime  vary,  a  com- 
mon practice  being  to  add  these  in  two  or  three  lots  and  not  all 
at  one  time.  In  this  case,  the  amount  added  each  time  depends 
upon  the  violence  of  the  reactions.  Whatever  method  is  used, 
the  purification  of  the  iron  is  quickly  effected,  if  the  slag  is  rich 
in  oxides  of  iron  and  the  percentage  of  impurities  of  the  hot 


OPEN-HEARTH  STEEL  179 

metal  added  is  considerably  reduced  by  dilution  with  the  puri- 
fied metal  in  the  furnace. 

Monell  Process.  — -  The  Monell  process  is  much  like  the  Tal- 
bot,  but  is  carried  out  in  a  stationary  furnace.  It  was  worked 
out  at  the  Carnegie  Steel  Co.'s  works,  and  depends  upon  the 
strong  oxidizing  action  of  a  slag  rich  in  oxides  of  iron.  The 
limestone  and  iron  oxides  are  charged  first,  and  when  these  are 
almost  melted,  molten  pig  iron  is  poured  into  the  furnace. 
The  entire  heat  is  tapped  when  it  is  purified.  The  excess  slag 
may  be  tapped  off  through  a  hole  placed  above  the  level  of  the 
metal,  but  its  flow  is  not  as  easily  controlled  as  when  a  tilting 
furnace  is  used;  besides,  the  rich  slag  corrodes  the  bottom,  thus 
necessitating  careful  attention  to  bottom  repairs. 

Bertrand-Thiel  Process.  —  In  the  Bertrand-Thiel  process,  two 
furnaces  are  used,  the  metal  being  transferred  from  the  " primary 
furnace,"  or  "  refiner,"  to  the  "  secondary  furnace,"  or  " fin- 
isher." It  was  invented  by  Messrs.  Bertrand  and  Thiel  of 
Austria,  in  1894,  and  may  be  worked  with  pig  iron  and  ore,  or 
pig  iron  and  scrap,  in  whatever  proportions  may  be  desired. 
The  furnaces  are  of  the  ordinary  open-hearth  type.  The  molten 
pig  iron  (or  pig  iron  and  scrap),  ore,  and  limestone  are  charged 
into  the  primary  furnace,  and  the  resulting  reaction  removes  all 
the  silicon,  most  of  the  phosphorus  and  manganese,  and  part  of 
the  carbon.  The  metal  is  then  run  into  the  finisher,  care  being 
taken  to  prevent  the  transfer  of  any  slag.  Lime,  ore,  and, 
as  a  rule,  scrap  heated  to  the  fusing  point  are  here  added  to  the 
bath.  As  the  slag  thus  formed  is  rich  in  oxides  of  iron,  the  car- 
bon and  remaining  phosphorus  are  quickly  removed. 

Duplex  Process.  —  In  the  duplex  process,  both  the  Bessemer 
converter  and  the  open-hearth  furnace  are  used.  This  method 
is  particularly  applicable  to  the  use  of  pig  iron  that  is  too  high  in 
silicon  to  be  worked  with  advantage  in  the  basic  Bessemer  or 
basic  open-hearth  process.  The  process  consists  in  removing 
all  the  silicon  and  part  of  the  manganese  and  carbon  in  an  acid 
converter,  and  then  decarburizing  and  dephosphorizing  this 
metal  in  the  basic  open-hearth  furnace.  In  the  United  States, 
the  process  is  used  mostly  in  the  Southern  fields  where  iron  ore 


l8o  IRON  AND   STEEL 

suitable  for  this  treatment  is  abundant.  In  1916,  3,436,457 
tons  of  steel  ingots  and  castings  were  made  by  the  duplex  process. 

Physical  Characteristics  of  Open-hearth  Steel.  —  According 
to  the  Manufacturers  Standard  Specifications  for  structural 
steel,  as  revised  April  21,  1914,  there  are  three  classes  of  struc- 
tural steel  as  previously  mentioned  in  Chapter  VII.  Class  A, 
which  is  used  for  railway  bridges  and  ships;  Class  B,  which  is 
used  for  buildings,  highway  bridges,  and  similar  structures; 
and  Class  C,  which  is  used  for  structural  rivets.  Classes  A 
and  C  must  be  made  by  the  open-hearth  process,  while  Class  B 
may  be  made  by  either  the  open-hearth  or  the  Bessemer  process. 

The  physical  properties  required  for  Class  A  and  B  steel  are 
as  follows:  Tensile  strength,  from  55,000  to  65,000  pounds  per 
square  inch;  maximum  yield-point,  one-half  of  the  tensile 
strength;  percentage  of  elongation  in  eight  inches  equals  a  mini- 
mum of  1,400,000  -T-  tensile  strength.  The  elongation  in  two 
inches  should  be  a  minimum  of  22  per  cent.  Class  B  steel  may 
have  a  tensile  strength  up  to  70,000  pounds  per  square  inch,  pro- 
vided the  elongation  is  not  less  than  the  percentage  required  for 
65,000  pounds  per  square  inch  tensile  strength. 

The  physical  properties  of  Class  C  steel  are  as  follows:  Ten- 
sile strength,  from  46,000  to  56,000  pounds  per  square  inch; 
maximum  yield-point,  one-half  of  the  tensile  strength;  percent- 
age of  elongation  in  eight  inches  equals  a  minimum  of  1,400,000 
-j-  tensile  strength.  With  regard  to  the  chemical  analysis,  the 
following  requirements  are  given: 

Class  A  Steel.  —  The  maximum  phosphorus  content,  when 
made  by  the  basic  open-hearth  process,  is  0.04  per  cent;  when 
made  by  the  acid  open-hearth  process,  0.06  per  cent.  The 
maximum  sulphur  content  is  0.05  per  cent. 

Class  B  Steel.  —  The  maximum  phosphorus  content,  when 
made  by  the  basic  open-hearth  process,  is  0.06  per  cent;  and 
when  made  by  the  acid  open-hearth  process,  0.08  per  cent.  The 
sulphur  content  is  not  specified. 

Class  C  Steel.  —  The  maximum  phosphorus  content,  when 
made  by  either  the  acid  or  the  basic  open-hearth  process,  is  0.04 
per  cent.  The  maximum  sulphur  content  is  0.045  Per  cent. 


CHAPTER  IX 
ELECTRIC   STEEL 

WHILE  electric  steel  or  steel  made  in  the  electric  furnace  is  not 
a  new  product,  the  expansion  of  this  branch  of  the  steel  industry 
has  been  very  rapid,  especially  since  1914.  In  1908  there  was 
only  one  furnace  in  the  United  States  producing  electric  steel 
and  the  output  for  the  year  was  only  about  55  tons.  The  num- 
ber of  electric  furnaces  operating  in  the  United  States  on  January 
i,  1918,  was  233  and  many  new  installations  have  been  made 
since  that  date.  The  estimated  tonnage  for  electric  steel  during 
1917  varies  greatly,  but  according  to  several  authorities  one 
million  tons  or  more  were  produced.  Whatever  the  rate  of 
production,  it  is  certain  that  the  electric  steel  industry,  which  a 
few  years  ago  was  in  the  experimental  stage,  is  now  on  a  firm 
commercial  basis. 

Early  experiments  in  the  production  of  electric  steel  were 
made  by  Sir  William  Siemens  who  constructed  a  small  arc 
furnace  in  1878.  Twenty  years  elapsed,  however,  before  the 
Stassano  furnace,  which  was  the  first  to  operate  commercially, 
was  introduced.  The  use  of  electric  furnaces  would  doubtless 
have  increased  more  rapidly  after  the  introduction  of  this  process 
had  it  not  been  for  the  relatively  high  cost  of  generating  elec- 
trical energy  at  that  time.  The  wonderful  advancement  made 
in  both  the  generation  and  distribution  of  electricity  during 
recent  years,  combined  with  the  advantages  of  the  electric  fur- 
nace for  certain  melting  and  refining  processes,  has  resulted  in 
the  rapid  development  of  this  method  of  producing  steel. 

Application  of  Electric  Furnaces   to  the  Steel   Industry. - 
Electric  furnaces  are  adapted  primarily  for  melting  and  refining 
processes,  and  they  probably  will  never  be  able  to  compete  with 
the  blast  furnace  for  smelting  ore  except  under  certain  favorable 
conditions.     What  might  be  defined  as  an  "  electric  blast  fur- 

181 


182  IRON  AND   STEEL 

nace"  was  developed  in  Sweden  in  1910.  This  furnace  is  similar 
in  principle  to  an  ordinary  blast  furnace,  except  that  it  is  pro- 
vided with  three  electrodes  which  take  the  place  of  the  tuyeres. 
The  furnace  operates  without  an  air  blast  and  either  charcoal  or 
coke  is  used  for  melting  the  charge  of  iron  ore.  The  charge  is 
fed  into  the  top  of  the  furnace  in  the  usual  way.  The  use  of  the 
electric  furnace  for  smelting  iron  ores  is  evidently  limited  to 
localities  where  hydro-electric  installations  and  cheap  electrical 
power  are  available.  One  electric  •  furnace  which  has  been  in- 
stalled in  the  United  States  and  is  used  for  smelting  has  a  rec- 
tangular steel  shell  lined  with  a  refractory  material  and  a  sloping 
bottom  to  facilitate  the  flow  of  the  molten  metal.  Five  stacks 
which  extend  above  the  roof  of  the  furnace  are  used  for  charg- 
ing and  graphite  electrodes  are  located  between  these  stacks. 
The  furnace  is  charged  at  regular  intervals  and  its  operation  is 
continuous. 

The  important  applications  of  electric  furnaces  in  the  steel 
industry  are  for  making  special  alloy  steels,  tool  steel  (including 
ordinary  carbon  steel  and  high-speed  steel),  for  melting  the  steel 
used  in  making  steel  castings,  and  for  melting  the  ferro-alloys 
which  are  added  to  "special  steels"  to  secure  different  chemical 
and  physical  properties.  Most  of  the  ferro-alloys  used  in  the 
United  States  prior  to  the  war  were  imported,  but  at  the  present 
time  large  quantities  of  the  alloys  used  in  producing  high-speed 
and  special  steels  are  manufactured  in  this  country.  These 
alloys  include  ferrosilicon,  ferrochrome,  ferronickel,  ferro- 
tungsten,  ferromanganese,  ferro vanadium,  etc.  The  electric 
furnace  has  also  been  used  to  a  limited  extent  for  refining  cupola 
iron  preparatory  to  making  malleable  castings. 

Most  of  the  electric  steel  produced  is  used  either  for  making 
special  alloy  steels  or  tool  steel,  although  the  electric  furnace  is 
used  extensively  in  steel  foundries.  No  accurate  data  is  avail- 
able as  to  the  amount  of  tool  steel  made  electrically  as  compared 
with  the  output  of  the  crucible  process.  Some  steel-makers  and 
metallurgists  contend  that  the  electric  furnace  not  only  produces 
much  more  tool  steel  at  the  present  time  than  the  crucible  process, 
but  that  ultimately  it  will  be  used  almost  exclusively  for  tool 


ELECTRIC  STEEL  183 

steel  production.  Others  connected  with  the  steel  industry  be- 
lieve that  there  will  continue  to  be  a  field  for  both  the  electric 
and  crucible  processes  and  that  the  electric  furnace  is  adapted 
more  especially  for  the  production  of  special  alloy  steels  for 
use  in  the  construction  of  automobiles,  airplanes,  ordnance, 
etc.  Steel  may  be  produced  in  the  electric  furnace  which  is 
undoubtedly  equal  to  crucible  steel  in  quality  if  not  superior  to 
it,  and  it  is  claimed  that  the  electric  process  is  more  economical, 
especially  at  the  present  time,  on  account  of  the  cost  of  crucibles. 
There  is  a  decided  difference  of  opinion  regarding  the  present  and 
future  use  of  the  electric  furnace  in  preference  to  the  open-hearth 
furnace.  Even  though  the  cost  of  electric  steel  is  higher  than  open- 
hearth  steel,  the  greater  degree  of  refinement  and  closer  regula- 
tion that  is  possible  with  the  electric  furnace  offset  this  difference 
of  cost  for  the  finer  grades  of  steel.  In  steel  foundry  practice, 
it  is  claimed  that  an  equivalent  tonnage  of  high-grade  electric 
steel  can  be  produced  at  an  average  lower  cost  than  the  ordinary 
commercial  grades  of  open-hearth  steel,  since  the  charge  of  the 
electric  furnace  may  consist  entirely  of  old  scrap  which  is  cheaper 
than  the  combined  scrap  and  pig  iron  required  with  the  other 
process.  One  of  the  striking  features  of  the  electric  furnace 
development  is  In  regard  to  the  size  of  the  installations.  A 
great  many  plants  are  now  equipped  with  furnaces  having  a 
capacity  of  five  or  six  tons,  but  ten,  fifteen,  and  twenty-five  ton 
sizes  are  in  use.  The  United  States  now  leads  in  the  number  of 
electric  furnaces  in  operation  and  Great  Britain  occupies  second 
place.  The  world's  largest  single  center  of  electric  steel  produc- 
tion, however,  is  in  Sheffield,  England. 

General  Classes  of  Electric  Furnaces.  —  Electric  furnaces  are 
used  either  for  melting  and  refining  metals,  or  for  heating  them 
to  some  temperature  below  the  melting  point,  as  in  connection 
with  the  heat- treatment  of  steel.  The  three  general  types 
in  use  may  be  classified  electrically  as  arc  furnaces,  resistance 
furnaces,  and  induction  furnaces.  With  each  type,  the  heat  is 
derived  from  electrical  resistance,  but  the  nature  or  form  of  the 
resistance  varies  in  the  different  general  classes  of  furnaces 
mentioned.  The  arc  furnace,  which  is  the  most  important 


1 84  IRON  AND   STEEL 

type  in  the  steel  industry  is  equipped  with  electrodes,  the  current 
passing  from  one  electrode  to  another.  These  furnaces  differ 
in  regard  to  the  arrangement  and  number  of  the  electrodes,  as 
explained  later.  The  arc  furnace  is  used  almost  exclusively  in 
the  production  of  electric  steel. 

While  all  electrical  furnaces  depend  upon  electrical  resistance, 
the  general  type  in  which  heat  is  generated  by  the  passage  of  a 
current  either  through  the  charge  or  through  a  resistor  forming 
part  of  the  furnace  is  classified  as  a  resistance  type  to  distinguish 
it  from  the  others.  Some  of  these  resistance  furnaces  are  so  ar- 
ranged that  electrodes  come  into  contact  with  the  charge  and  the 
latter  forms  the  resistance.  This  is  the  direct  resistance  class. 
Another  type  has  a  resistor  which  surrounds  the  furnace  crucible 
and  heats  it  by  direct  radiation,  and  there  is  a  third  class  in  which 
the  heat  generated  in  the  graphitic  or  other  resistor  is  radiated  to 
the  walls  of  the  furnace  and  te  then  reflected  onto  the  charge. 
Resistance  furnaces  in  general  are  used  principally  for  heat- 
treating,  annealing,  and  for  melting  nonferrous  metals. 

With  the  induction  type  of  furnace,  the  heat  is  generated  in 
the  metallic  charge  by  means  of  induced  currents.  This  type 
is  similar  in  principle  to  a  static  transformer,  the  material  heated 
corresponding  to  the  low  tension  winding.  Thus,  the  induction 
furnace  may  be  denned  as  an  electrical  apparatus  which  con- 
tains within  itself  the  transformer  that  induces  the  heat  in  the 
charge,  whereas  the  arc  furnace  is  practically  a  hearth  which 
holds  the  charge,  and  the  arc  is  the  source  of  heat  and  serves 
the  same  purpose  as  the  flame  in  an  open-hearth  furnace.  The 
first  induction  furnace  for  steel  melting  was  developed  by  Kjellin, 
in  Sweden,  about  1900.  The  primary  winding  of  a  Kjellin 
type  surrounds  the  core  and  is  within  a  cylinder  made  of  re- 
fractory material  and  cooled  either  by  circulating  water  or  a 
forced  draft.  The  annular  shaped  hearth  containing  molten 
metal  is  beyond  the  windings  and  acts  as  a  single  turn  of  the 
secondary  winding;  consequently,  when  current  flows  through 
the  primary  winding,  a  current  is  induced  in  the  bath  of  metal 
which  is  thereby  heated,  practically  all  of  the  electrical  energy 
being  converted  into  heat.  Induction  furnaces  are  used  very 


ELECTRIC  STEEL  185 

little  in  steel  plants,  but  are  applied  principally  in  melting  non- 
ferrous  metals. 

Methods  of  Operating  Electric  Furnaces.  —  Electric  furnaces 
may  either  melt  a  cold  charge  or  they  may  receive  the  metal  in  a 
molten  condition.  Most  of  the  electric  furnaces  now  in  use  are 
for  cold  melting,  but  the  larger  sizes  are  commonly  arranged  to 
use  molten  charges.  After  the  introduction  of  the  electric 
furnace,  steel  manufacturers  soon  recognize.d  that  it  might  be 
used  to  advantage  in  conjunction  with  the  Bessemer  converter 
and  open-hearth  furnace,  following  the  plan  of  the  well-known 
"duplex  process"  by  which  the  metal  is  partly  purified  in  a 
Bessemer  converter  and  is  then  further  refined  in  the  open-hearth 
furnace.  In  fact,  the  first  electric  furnace  installation  in  the 
United  States  consisted  of  an  open-hearth  furnace  for  prelimi- 
nary melting  and  refining,  and  an  electric  furnace  which  re- 
ceived the  molten  metal  for  deoxidizing  and  desulphurizing  it  and 
for  making  whatever  additions  or  changes  might  be  necessary  to 
secure  the  desired  analysis.  This  is  often  called  the  "hot  metal 
process."  Both  Bessemer  converters  and  open-hearth  furnaces 
are  also  used  in  conjunction  with  the  electric  furnace.  The 
Bessemer  converter  is  used  for  decarbonizing  and  desiliconizing 
the  metal;  the  open-hearth  furnace  is  then  used  for  dephos- 
phorizing it,  and  the  refining  process  is  then  completed  by  deox- 
idizing and  desulphurizing  in  the  electric  furnace.  One  instal- 
lation operating  on  the  triplex  system  consists  of  ten  electric 
furnaces  having  a  nominal  capacity  of  25  tons  each,  two  25-ton 
open-hearth  furnaces,  and  two  25-ton  Bessemer  converters,  the 
three  processes  being  used  in  tandem.  The  metal  is  first 
"blown"  in  the  Bessemer  converter.  Then  it  is  transferred  to 
the  open-hearth  furnaces  and  finally  to  the  electric  furnaces. 
The  estimated  capacity  of  this  plant  is  50,000  tons  of  electric 
furnace  steel  per  month. 

Electric  furnaces  may  either  be  basic  or  acid,  but  a  large 
percentage  are  lined  for  basic  operation.  The  basic  furnace 
permits  the  use  of  a  basic  slag  which  serves  to  remove  impurities 
from  the  metal,  just  as  in  the  basic  open-hearth  furnace.  Thus 
phosphorus,  sulphur,  and  oxygen  may  be  removed,  which  per- 


1 86  IRON  AND   STEEL 

mits  using  relatively  cheap  raw  materials.  With  tne  acid  process, 
no  phosphorus  or  sulphur  is  removed,  and  if  these  elements  are 
to  be  held  within  narrow  limits,  the  materials  composing  the 
charge  must  be  carefully  selected. 

Advantages  of  the  Electric  Process.  —  The  steel  produced  in 
the  electric  furnace  may  be  chemically  purer  than  that  made  by 
any  other  process,  although  it  does  not  necessarily  follow  that 
electric  steel  has  superior  physical  qualities  simply  because  it  is 
pure  chemically.  Inferior  grades  of  steel  may  be  produced  in 
the  electric  furnace,  and  the  extremely  high  temperatures  ob- 
tained from  the  electric  arc  are  often  referred  to  as  the  principal 
cause  of  poor  electric  steel.  The  fact  remains,  however,  that 
the  electric  furnace  when  properly  designed  and  used  is  capable 
of  producing  steel  which  chemically  or  physically  is  unexcelled. 
One  advantage  of  the  electric  furnaces  is  that  they  permit  of 
closer  control  of  the  composition  of  steel  than  any  other  process, 
which  accounts  for  their  use  for  instance  in  preference  to  the 
open-hearth  furnace  in  the  production  of  special  alloy  steels. 
In  the  electric  furnace,  since  the  heat  is  obtained  from  the  elec- 
tric current  and  no  fuel  is  burned,  there  are  no  impurities  intro- 
duced from  the  gases  of  combustion;  in  fact,  fusion  may  be 
effected  in  a  neutral  or  reducing  atmosphere.  Less  excess  alloy 
needs  to  be  added  to  the  heat  in  an  electric  furnace  to  insure 
the  proper  amount  in  the  finished  steel.  Some  steel-makers 
claim  that  it  is  necessary  to  use  only  one-half  the  amount  of 
ferromanganese  that  would  be  required  with  the  best  open- 
hearth  practice.  Another  point  in  favor  of  the  electric  furnace 
is  that  the  alloy  additions  for  making  alloy  steels  may  be  made 
in  the  furnace  itself,  rather  than  in  the  ladle,  thus  insuring 
thorough  assimilation,  diffusion,  and  a  more  homogeneous 
product. 

Accurate  control  of  the  composition  of  electric  steel  tends  to 
make  the  results  of  heat-treatment  more  certain,  and  it  may  be 
subjected  to  a  higher  degree  of  heat  without  injury  in  forging  or 
in  connection  with  heat-treatment  than  is  the  case  with  other 
steels.  The  electric  furnace  also  has  an  advantage  in  that  it  may 
be  used  in  recovering  alloy  scrap,  which,  in  some  cases,  is  not 


ELECTRIC  STEEL  187 

desirable  to  include  in  the  charge  of  an  open-hearth  furnace. 
Furthermore,  when  alloy  scrap  is  used  in  an  open-hearth  fur- 
nace, a  large  proportion  of  the  alloy  metal  is  lost  in  the  slag.  It 
is  practicable  to  use  relatively  cheap  raw  materials  in  the  elec- 
tric furnace  and  to  convert  them  into  high-grade  steel,  which 
can  be  deoxidized  and  desulphurized  almost  completely.  The 
phosphorus  and  sulphur  may  not  exceed  o.oio  per  cent,  and  in 
carbon  steel  the  average  sulphur  content  is  lower,  whereas,  in 
alloy  steels,  the  sulphur  barely  exceeds  0.015  Per  cent. 

Tests  of  electric  and  open-hearth  steels  each  having  a  carbon 
content  of  o.  1 2  per  cent  showed  the  following  physical  properties : 
Ultimate  strength  of  open-hearth  steel,  56,500  pounds  per  square 
inch;  elongation  in  two  inches,  29.82  per  cent;  ultimate  strength 
of  electric  steel,  65,200  pounds  per  square  inch;  elongation  in 
two  inches,  26.05  Per  cent-  When  the  carbon  content  was  in- 
creased in  each  case  to  0.20  per  cent,  the  ultimate  strength 
of  the  open-hearth  steel  was  58,320  pounds  per  square  inch; 
and  the  elongation  in  two  inches,  28.35  Per  cent.  The  ultimate 
strength  of  the  electric  steel  was  73,150  pounds  per  square  inch, 
and  the  elongation  in  two  inches,  22.75  Per  cent. 

Types  of  Arc  Furnaces  Used  in  the  Steel  Industry.  —  Since 
the  arc  furnace  is  used  almost  exclusively  in  the  steel  industry, 
only  this  general  type  will  be  considered.  All  arc  furnaces  may 
be  divided  into  two  classes,  first,  the  arc  radiation  class  and, 
second,  the  arc  resistance  or  arc  conduction  class.  Furnaces  of 
the  second  class  may  belong  either  to  the  short  arc  type  or  the 
long  arc  type.  The  Stassano  furnace,  which  was  the  first  com- 
mercial design,  heated  the  metal  almost  entirely  by  radiation 
from  the  electric  arc  and  it  belongs  to  the  arc  radiation  class. 
The  arc  resistance  type  is  so  arranged  that  heat  is  generated  by 
the  arc  and  by  the  passage  of  current  through  the  charge.  The 
current  may  either  pass  along  the  surface  of  the  charge  to  the 
other  electrodes  or  through  the  body  of  the  charge. 

The  arc  furnace  may  use  either  direct  or  alternating  current, 
the  latter  being  used  largely  since  this  is  the  current  supplied 
by  most  power  companies.  The  three-phase  current  is  employed 
more  than  the  two-phase  or  single-phase.  The  voltage  depends 


i88 


IRON   AND    STEEL 


upon  the  length  of  the  arc,  as  the  latter  is  a  form  of  electrical 
resistance.  Whatever  voltage  is  required  for  melting  or  heating 
is  obtained  by  transformers  at  the  furnace,  so  that  the  transmis- 
sion voltage  may  be  of  any  value. 

Heroult  Electric  Furnace.  —  The  Heroult  furnace,  which  is 
now  used  more  than  any  other  type,  belongs  to  the  arc  resistance 
class.  The  electrodes  are  ulaced  above  the  bath  and  the  cur- 


Machinery 


Fig.   i. 


Small  Heroult  Furnace  and  its  Electrically-operated 
Tilting  Mechanism 


rent  passes  from  one  electrode  to  the  metal  and  from  the  metal  to 
the  next  electrode.  In  this  way,  the  bath  is  heated  both  by  the 
heat  radiated  from  the  arc  and  by  the  heat  produced  by  the 
resistance  of  the  steel  and  the  slag  to  the  passage  of  the  current 
through  them.  Fig.  i  shows  a  sectional  view  of  a  three-phase 
Heroult  furnace  and  its  electrically-operated  tilting  mechanism. 
The  three  electrodes  extend  down  through  the  roof  of  the  fur- 


ELECTRIC   STEEL 


189 


nace  and  are  so  located  that  lines  joining  their  centers  would 
form  a  triangle.  The  steel  shell  of  the  furnace  is  lined  with  a 
refractory  material,  the  exact  nature  of  which  depends  upon 
whether  the  furnace  is  to  be  basic  or  acid  in  its  operation.  The 
three  electrodes  are  connected  with  the  transformers  by  flexible 
cables  which  permit  the  furnace  to  be  tilted  while  pouring  the 
charge.  The  furnace  shown  in  Fig.  i  is  so  arranged  that  it 
tilts  about  a  hinge  located  just  below  the  spout  so  that  the  latter 
remains  nearly  stationary  while  pouring.  The  dotted  lines  in- 


Fig.  2.     Twenty-five  ton  Heroult  Furnace  receiving  Charge  of 
Molten  Metal 

dicate  the  pouring  position.  Power  for  tilting  the  furnace  is 
derived  from  a  motor  which  transmits  motion  to  a  large  gear 
wheel  through  a  combination  of  spur  and  worm  gearing.  This 
gear  wheel  is  connected  directly  with  the  furnace  by  means  of 
rods,  as  the  illustration  shows.  One  advantage  of  this  arrange- 
ment is  that,  if  the  operator  fails  to  stop  the  motor,  the  furnace 
will  simply  descend  to  its  original  position;  moreover,  when  the 
furnace  is  either  at  the  upper  or  lower  positions  of  the  stroke, 
it  will  move  in  the  desired  direction,  no  matter  which  way  the 


IRON  AND   STEEL 


controller  is  operated.  The  weight  of  the  furnace  is  balanced 
by  a  counterweight  which  connects  by  means  of  levers. 

The  25-ton  Heroult  furnace  illustrated  in  Figs.  2  and  3  is  the 
largest  size  in  use  at  the  present  time.  Fig.  2  shows  a  charge 
of  molten  metal  being  poured  from  the  ladle  into  the  furnace, 
and  Fig.  3  shows  the  furnace  tilted  and  the  refined  charge  being 
poured. 

Snyder  Electric  Furnace.  —  The  Snyder  electric  furnace  be- 
longs to  the  arc  resistance  class  and  is  a  long  arc  type.  The 


Fig.  3.     Twenty-five-ton  Heroult  Furnace  in  Pouring  Position 

electric  current  may  be  either  single-phase,  two-  or  three-phase, 
or  direct-current,  but  the  latter  is  not  commonly  used.  The 
single-phase  or  direct-current  furnaces  have  two  electrical  con- 
nections, whereas  the  two-  or  three-phase  furnaces  have  three 
or  more,  according  to  the  type.  The  three-phase  furnace  has 
two  of  the  phases  connected  to  the  movable  carbon  electrodes 
at  the  top,  while  the  third  is  connected  to  a  metal  contact  at  the 
bottom  of  the  furnace.  The  Snyder  furnace  is  doorless,  and  the 
entire  roof  of  the  furnace  is  tilted  back  for  charging,  as  shown  by 
the  illustration,  Fig.  4.  After  the  charge  has  been  dropped  into 


ELECTRIC   STEEL 


191 


the  furnace,  the  roof  is  pulled  forward  by  a  motor  and  sealed 
with  a  dry  fireclay  gasket.  The  electrodes  may  be  either  hand  or 
motor  operated,  an  automatic  regulator  being  applied  in  the  case 
of  motor  operation.  An  advantage  claimed  for  the  long  arc  is 
that  it  minimizes  the  necessity  of  moving  the  electrodes.  The 
opening  roof  feature  also  reduces  the  time  for  charging,  since 


Fig.  4.     Five-ton  Snyder  Furnace  with  Roof  tilted  back  for  Charging 

machinery  can  be  used  instead  of  shovels.  These  furnaces  are 
arranged  in  three  different  ways  to  meet  the  pouring  require- 
ments under  different  conditions.  With  the  rocking  type, 
which  is  illustrated  in  Fig.  4  and  is  the  most  common,  the  end  of 
the  spout  moves  forward  and  down  as  the  furnace  is  tilted  to  the 
pouring  position.  This  type  is  recommended  when  it  is  rela- 
tively easy  to  move  the  ladle  to  correspond  with  the  movement 


IQ2 


IRON  AND   STEEL 


of  the  spout.  The  second  or  " heaving"  type  has  a  circular 
shaped  rocker  underneath  the  furnace  which  is  so  located  that 
the  spout  remains  practically  stationary  as  the  furnace  is  tilted. 
This  arrangement  is  especially  adapted  for  hand  ladle  work. 
With  the  third  or  " dumping"  type,  the  spout  moves  down  and 
backward.  This  type  is  ordinarily  preferred  for  small  instal- 
lations in  which  it  is  easy  to  follow  the  spout  with  hand  ladles. 


Machinery 


Fig.  5.     Sectional  View  illustrating  Arrangement  of  Flectrodes 
in  Rennerfelt  Furnace 

Rennerfelt  Electric  Furnace.  —  The  Rennerfelt  electric  fur- 
nace operates  with  a  free  burning  arc  like  the  Stassano  furnace, 
but  differs  from  the  latter  in  the  way  the  arc  is  formed.  A 
cross-sectional  view  of  a  three  gross- ton  size  is  shown  in  Fig.  5. 
There  are  three  electrodes,  a  vertical  electrode  being  placed  be- 
tween two  electrodes  which  are  shown  in  a  horizontal  position, 
but  may  be  tilted,  as  explained  later.  The  vertical  electrode 
carries  about  40  per  cent  more  current  than  the  others,  so  that 
the  arc  is  thrown  downward  toward  the  bath  and  away  from  the 


ELECTRIC   STEEL 


193 


roof  of  the  furnace.  The  three-phase  current,  which  may  be  of 
any  voltage  and  frequency,  is  transformed  to  a  two-phase  three- 
wire  system.  The  two  side  electrodes  are  connected  to  the  ter- 
minal of  each  phase,  and  the  top  electrode  is  connected  to  the 
middle  conductor.  The  power  input  is  regulated  by  moving  the 
side  electrodes  in  or  out,  thus  changing  the  length  of  the  arc. 
This  adjustment  may  be  effected  by  hand  or  by  electric  motors 
controlled  either  automatically  or  by  means  of  push-buttons.. 
The  top  electrode  has  to  be  moved  downward  perhaps  once  an 


Fig.  6.    Front  View  of  One-ton  Rennerfelt  Furnace 

hour,  depending  upon  its  consumption.  When  charging  the 
furnace,  the  side  electrodes  are  tilted  upwards,  thus  leaving 
sufficient  space  beneath  for  inserting  the  whole  charge  at  one 
time.  As  the  charge  melts,  the  electrode  ends  are  continually 
lowered,  thus  keeping  the  flame  about  two  or  three  inches  over 
the  bath.  A  one- ton  Rennerfelt  furnace  is  shown  in  Fig.  6. 
The  electrodes  at  the  sides  and  their  holders,  and  the  upper  ver- 
tical electrode,  may  be  seen  in  this  illustration.  These  furnaces 
are  provided  with  trunnions  resting  on  roller  bearings  supported 


194 


IRON  AND   STEEL 


by  frames  at  the  sides  and  they  are  tilted  either  by  hand  or  by 
motors,  depending  upon  the  size.  The  furnaces  with  a  capacity 
up  to  one  ton  have  only  one  working  door  which  is  used  both  for 
charging  and  pouring;  the  larger  furnaces  have  one  charging  and 
one  pouring  door. 

Booth-Hall  Electric  Furnace.  —  The  Booth-Hall  furnace  (see 
Fig.  7)  is  so  arranged  that  power  is  introduced  through  one,  two, 


Fig.  7.    Booth-Hall  Furnace  of  Four-ton  Capacity 

or  three  main  vertical  electrodes,  the  number  depending  upon 
whether  the  furnace  is  to  operate  single-phase,  two-phase,  or 
three-phase.  The  furnace  also  has  an  auxiliary  electrode  and 
wrought-iron  grids  which  are  imbedded  in  a  hearth  with  a  re- 
fractory facing.  The  auxiliary  electrode  is  inserted  vertically 
through  the  roof,  except  in  small  furnaces,  in  which  case  it  is 
inserted  obliquely  through  the  door  opening.  The  two-phase 


ELECTRIC  STEEL  195 

furnace  is  considered  preferable  for  the  usual  power  supply  and 
steel  refining  conditions,  and  the  following  description  applies 
particularly  to  this  class: 

When  starting  a  heat  in  a  two-phase  furnace  with  a  cold  charge, 
a  pawl  on  the  auxiliary  electrode  holder  is  released,  permitting  the 
electrode  to  rest  upon  the  scrap  charge.  Arcs  are  then  drawn 
with  the  two  main  electrodes  and  the  metal  begins  to  melt  under 
these  arcs.  The  auxiliary  electrode  acts  as  a  common  neutral 
or  return,  no  arc  being  drawn,  and  consequently  no  melting  oc- 
curs under  the  auxiliary  electrode.  When  enough  molten  metal 
has  accumulated  on  the  hearth  to  make  the  latter  a  conductor 
of  electricity,  the  current  begins  to  flow  through  the  wrought- 
iron  grids.  The  auxiliary  electrode  is  then  withdrawn  from  the 
furnace  entirely,  and  the  opening  for  it  is  closed.  The  fur- 
nace then  continues  to  operate,  the  current  passing  through  the 
main  vertical  electrode,  the  bath,  and  the  hearth,  and  out  through 
the  grids.  The  transformer  connections  are  so  arranged  that 
each  of  the  two  phases  has  an  independent  circuit.  The  arcs 
are  governed  by  automatic  electrode  regulators  for  maintaining 
a  uniform  power  input  into  the  furnace  and  a  balanced  load  on 
the  lines. 

Since  there  are  only  two  electrodes  entering  the  roof  of  a  two- 
phase  furnace  except  at  the  beginning  of  a  heat,  it  is  claimed  that 
the  furnace  has  a  relatively  low  radiation  loss,  less  electrode 
breakage  and  electrode  consumption,  as  well  as  a  lower  initial 
cost  for  the  furnace  equipment,  as  compared  with  types  having 
three  or  four  main  electrodes.  The  possibility  of  failure  to 
secure  contact  when  starting  a  heat  is  said  to  be  eliminated  by 
the  use  of  the  auxiliary  electrode.  The  two  main  electrodes  and 
the  auxiliary  electrode  acting  as  a  common  neutral  makes  it 
possible  to  use  the  arcs  for  sintering  in  the  hearth  of  the  furnace 
layer  by  layer,  thus  forming  a  monolithic  mass  that  is  durable. 
All  the  tilting  and  electrode  regulating  mechanism  is  below  the 
floor  and  is  completely  covered.  Furnaces  ranging  from  2%  to  6 
tons  capacity  are  built  two-phase,  since  in  practically  all  lo- 
calities a  single-phase  load  for  such  furnaces  would  not  be  ac- 
ceptable to  power  companies.  For  refining  steel,  the  two-phase 


IRON  AND   STEEL 

furnace  is  recommended,  except  in  8  and  10  ton  sizes,  in  which 
case  the  three-phase  type  is  regarded  as  more  practicable.  Fur- 
naces up  to  1 1  ton  holding  capacity  intended  for  the  straight 
melting  of  scrap  are  made  single-phase,  unless  power  conditions 
are  such  that  a  single-phase  load  is  not  acceptable. 

Ludlum  Electric  Furnace.  —  The  Ludlum  electric  furnace  is 
an  ellipsoidal  form  and  it  has  three  electrodes  which  extend  down 


Fig.  8.     Ten-ton  Ludlum  Furnace  in  Pouring  Position 

through  the  roof.  These  electrodes  instead  of  being  located  in 
triangular  formation  are  in  a  straight  line  corresponding  to  the 
center  line  of  the  furnace  (see  Fig.  8  which  shows  a  lo-ton  fur- 
nace in  the  pouring  position).  The  electrodes  are  held  by 
bronze  arms  projecting  from  upright  beams  attached  to  the 
furnace  structure.  These  arms  may  be  raised  and  lowered  by 
the  automatic  control  or  by  handwheels.  There  are  no  bottom 


ELECTRIC   STEEL 


197 


connections.  The  shape  of  the  furnace  is  such  that  there  are  no 
straight  side  walls  nor  over-hanging  walls  with  the  furnace  in 
any  working  position.  There  is  a  door  at  each  end  of  the  fur- 
nace but  no  spout.  The  furnace  can  be  charged  from  both 
ends  at  once,  and  it  is  tilted  by  an  electric  motor  to  pour  through 
one  of  the  doors. 


Fig.  9.     Three-ton  Greaves-Etchells  Furnace 

The  furnace  is  filled  with  the  charge  of  scrap  to  be  melted, 
and  at  first  the  electrodes  rest  on  the  charge  so  that  soon  after 
the  current  is  turned  on  the  electrodes  melt  their  way  through 
nearly  to  the  bottom.  By  this  time,  a  pool  of  molten  metal  has 
formed  beneath  the  electrodes  because  the  deepest  part  of  the 
hearth  is  directly  below  them.  The  charge  is  melted  from  the 
bottom  up,  the  arcs  remaining  covered  by  the  scrap  until  the 
latter  is  completely  melted,  so  that  the  roof  is  not  exposed  to 


IRON  AND   STEEL 


the  high  temperature  radiating  from  an  open  arc.  The  roof  of 
this  furnace  is  in  the  form  of  a  low  arch  and,  in  practice,  an  extra 
roof  is  built  on  a  separate  frame,  so  that  the  old  one  can  readily 
be  replaced  at  any  time.  For  basic  operation,  the  hearth  is 
lined  with  magnesite  brick  to  a  thickness  of  9  inches  or  more. 
Greaves-Etchells  Electric  Furnace.  —  The  Greaves-Etchells 
furnace  has  two  of  the  phases  connected  to  the  two  electrodes 
above  the  bath  while  the  third  phase  is  connected  to  a  copper 


Machinery 


Fig.   10. 


Diagram  illustrating  Arrangement  of  Twelve-ton 
Greaves-Etchells  Furnace 


plate  which  extends  over  the  bottom  of  the  furnace.  (See  Fig. 
9  and  also  the  diagram,  Fig.  10.)  The  current  flowing  through 
the  hearth  generates  considerable  heat  below  the  bath  and  the 
electric  arcs  above  the  charge  maintain  the  slag  and  surface  at 
the  desired  temperature.  Convection  currents  in  the  metal,  re-, 
suiting  from  the  bottom  heating,  cause  a  continuous  circulation 
of  the  metal  and  uniform  heating.  The  hearth  lining,  which  is 
at  least  20  inches  thick,  is  made  of  dolomite,  magnesite,  and  other 
materials,  in  such  a  way  that  the  electrical  resistance  is  high  at 


ELECTRIC   STEEL 


199 


the  inside  of  the  bath  in  proximity  to  the  charge  and  decreases 
rapidly  to  a  negligible  quantity  at  the  outside.  The  system  of 
transformer  ratios  is  arranged  to  give  a  balanced  condition  when 
the  upper  electrodes  are  in  equal  adjustment.  The  equipment 
has  been  designed  to  withstand  any  short-circuiting  of  the  elec- 
trodes which  may  occur  during  the  melting  process  when  pieces 
of  scrap  fall  against  the  electrodes.  The  transformer  connections 
are  such  that  the  short-circuit  current  of  one  electrode  must 
traverse  two  transformers  in 
series  and  in  different  phase 
which  automatically  lowers 
the  power  factor  momentarily 
and  has  a  strong  buffer  effect; 
moreover,  the  permanent  re- 
sistance in  the  path  of  the 
current  through  the  hearth 
also  limits  the  effect  of  short 
circuits.  The  raising  or  lower- 
ing of  the  electrode  for  reg- 
ulating the  energy  supplied  by 
the  furnace  may  be  effected 
by  automatic  regulators  or  by 
hand  control.  The  voltages  Machinery 


across    the    arcs   may   also    be       Fig.  u.      Diagram  showing  Arrange- 

varied  in  all  except  the  smallest     ment  of  Electrodes  in  Girod  Furnace 
size  of  furnace,  and  the  ratio  of  heat  generated  above  and  below 
the  bath  may  be   regulated  over  a  wide  range.     The  tilting 
mechanism  is  so  arranged  that  the  spout  travels  downwards  in 
a  vertical  line  when  pouring. 

Girod  Electric  Furnace.  —  The  Girod  electric  furnace  is  an 
arc  conduction  type  of  the  class  having  bottom  connections. 
The  current  is  supplied  by  one  or  more  carbon  electrodes  A 
(see  Fig.  n)  which  extend  down  through  the  furnace  roof. 
The  lower  ends  of  these  electrodes  are  near  the  level  of  the  slag 
as  in  other  furnaces.  In  the  bottom  of  the  furnace  and  as  far  as 
possible  from  the  upper  carbon  electrodes,  there  are  six  or  more 
steel  electrodes  B  which  pass  through  the  refractory  bottom  and 


200  IRON  AND   STEEL 

are  in  direct  connection  with  the  furnace  shell  and  the  low-ten- 
sion side  of  the  power  plant.  With  this  arrangement,  the  cur- 
rent is  forced  to  pass  through  the  charge,  the  object  being  to 
obtain  a  more  uniform  heat  than  when  the  arc  is  formed  above 
the  charge  or  passes  through  the  upper  surface.  Another  ad- 
vantage claimed  for  the  Girod  furnace  is  that  the  current  passing 
through  the  bath  produces  an  electromagnetic  field  which  gives 
the  bath  a  rotary  movement  and  accelerates  chemical  reaction. 

The  Girod  furnace  may  be  adapted  to  any  system  of  current, 
and  the  usual  tension  is  65  volts  for  small  furnaces  and  70  volts 
for  large  ones.  The  use  of  single-phase  alternating  current  is 
considered  preferable  for  furnaces  of  small  capacity.  Furnaces 
up  to  four  tons  in  capacity  are  generally  single-phase  and 
have  one  carbon  electrode,  whereas  larger  sizes  are  three-phase 
and  have  three  carbon  electrodes.  The  use  of  a  single-phase 
furnace  involves,  in  a  three-phase  distribution  system,  the  in- 
stallation of  rotary  converters  or  motor  generators  with  trans- 
formation losses  of  about  14  per  cent.  The  three-phase  furnace 
simply  requires  step-down  transformers  with  energy  losses  of 
only  3  or  4  per  cent.  The  connections  of  a  three-phase  furnace 
are  arranged  to  give  an  equal  load  on  each  phase.  The  furnace 
is  fitted  with  a  sliding  door  through  which  the  charge  is  inserted 
and  the  slag  removed.  Opposite  the  door  is  the  tap  hole. 

Electrodes  for  Electric  Furnaces  and  Their  Regulation.  - 
The  electrodes  used  in  electric  furnaces  for  steel  melting  and 
refining  are  made  either  of  amorphous  or  graphitic  carbon.  The 
graphite  electrodes  are  generally  used  on  the  long  arc  type  of 
furnace,  but  many  short  arc  furnaces  are  provided  with  amor- 
phous carbon  electrodes,  because  of  the  " umbrella"  effect,  since 
they  are  twice  as  large  in  diameter  as  the  graphite  electrodes  and 
afford  better  protection  for  the  roof  against  the  intense  heat 
radiated  directly  from  the  arc.  While  the  electric  conductivity 
of  graphite  is  much  higher  than  that  of  amorphous  carbon,  the 
former  is  more  expensive.  The  number  of  electrodes  depends 
upon  the  kind  of  current  used  and  whether  or  not  there  are 
electrical  connections  through  the  bottom  of  the  furnace.  With 
bottom  connections,  a  single-phase  furnace  requires  one  elec- 


ELECTRIC   STEEL  2OI 

trode;  a  two-phase  furnace,  two  electrodes;  and  a  three-phase 
furnace,  three  electrodes.  If  there  are  no  bottom  connections 
and  the  current  either  passes  from  one  electrode  to  the  other 
through  the  bath  or  is  arranged  to  maintain  the  arc  above 
and  clear  of  the  bath,  then  a  single-phase  furnace  requires  two 
electrodes;  a  two-phase  furnace,  four  electrodes;  and  a  three- 
phase  furnace,  three  electrodes. 

The  adjustment  of  the  electrodes  to  regulate  the  length  of 
arc  and  the  flow  of  the  current  may  be  effected  by  hand,  but  an 
automatic  regulating  device  is  generally  employed.  Hand  regu- 
lation involves  constant  attention  on  the  part  of  the  operator, 
and  is  laborious  on  the  large  furnaces  so  that  automatic  regulation 
is  preferable.  The  Thury  system  of  regulation,  as  applied  to  a 
three-phase  furnace,  has  three  regulators,  there  being  one  for 
each  electrode.  The  electrodes  are  maintained  in  the  desired 
positions  by  means  of  these  regulators  in  conjunction  with  the 
motor-driven  electrode  adjusting  mechanism.  The  regulators 
are  connected  to  a  motor-driven  countershaft,  and  each  regulator 
is  in  the  form  of  a  double-throw  switch  for  rotating  the  motor  in 
either  direction.  The  operation  of  this  switch  is  controlled  by  a 
solenoid  which  is  energized  by  current  from  a  series  transformer 
in  the  main  circuit  on  the  high-tension  side.  The  regulating 
mechanism  controlling  the  switch  is  held  in  equilibrium  when 
the  flow  of  the  current  is  normal.  Any  decided  variation  in 
the  flow  causes  the  regulator  switch  to  be  thrown  in  whatever 
direction  is  required  to  restore  the  normal  current  flow  by  ad- 
justing the  electrodes.  The  electrode  holders  should  be  water- 
cooled  in  order  to  prevent  arcing  at  the  connections,  although 
this  may  not  be  necessary  on  very  small  furnaces. 

The  automatic  electrode  control  made  by  the  General  Electric 
Co.  has  a  control  panel  consisting  of  three  sections.  On  the 
upper  section  are  located  three  electrode  groups,  each  consisting 
of  one  contactor  group  and  one  shunt  relay.  This  shunt  relay 
is  connected  across  the  alternating-current  circuit  and  if  the 
latter  is  broken  or  the  power  fails  for  any  reason,  the  relay  opens 
the  control  circuits,  thus  preventing  damage  to  the  furnace 
and  loss  of  heat.  The  contactor  group  consists  of  one  raising 
13  * 


202  IRON  AND   STEEL 

contactor,  one  lowering  contactor,  and  one  dynamic  breaking 
contactor,  all  mechanically  interlocked.  On  the  middle  section 
of  the  panel  there  is  a  glass  case  containing  three  contact-making 
ammeters,  each  controlling  one  contactor.  Below  each  ammeter 
there  is  a  dial  switch  for  varying  the  number  of  effective  turns 
in  the  ammeter  coil  and  in  this  way  the  amount  of  power  fed 
to  the  furnace.  (A  more  recent  design  is  equipped  with  a 
rheostat  in  shunt  with  the  ammeter  coil.)  On  the  bottom  sec- 
tion of  the  panel,  there  are  four  double-pole  single-throw  switches. 
One  of  these  is  a  totalizing  switch  for  the  electrode  motors,  each 
motor  being  controlled  by  one  of  the  three  additional  switches. 
On  the  back  of  the  panel,  three  contactors  are  located  for 
varying  the  resistance  in  series  with  the  electrode  motors  when 
changing  from  normal  to  the  emergency  conditions,  and  vice 
versa. 

Electric  Furnace  Linings.  —  Magnesite  and  silica  are  the  prin- 
cipal materials  used  for  electric  furnace  linings.  In  a  basic 
furnace,  the  lining  of  the  hearth  and  up  to  a  point  a  little  above 
the  slag  line  is  usually  of  magnesite,  although  dolomite  may 
also  be  used.  The  furnace  wall  above  the  slag  line  may  be  lined 
with  silica,  magnesia,  or  chrome  brick,  the  material  being  se- 
lected according  to  conditions.  Silica  is  used  for  the  roof  lining 
of  a  basic  furnace,  and  an  acid  furnace  is  lined  with  silica  through- 
out. 

The  Rennerfelt  furnace  illustrated  in  Fig.  5  is  lined  for  basic 
operation.  Firebrick  is  placed  next  to  the  shell  as  indicated 
by  the  single  section  lines.  The  next  layer,  which  extends 
slightly  above  the  slag  line,  consists  of  magnesite  bricks  (in- 
dicated by  cross-hatching  or  double  section  lines)  and  an  inner 
fused  lining  of  dead  burned  magnesite.  The  side  walls  from  the 
point  where  the  magnesite  bricks  end,  up  to  the  roof,  are  lined 
with  silica  bricks  which  are  also  used  for  the  roof.  For  acid 
operation,  the  bottom  of  the  furnace  would  be  made  up  of  silica 
bricks  with  a  fused  lining  of  ganister  on  top,  and  the  walls  and 
roof  would  be  lined  with  silica  brick. 

Electric  Furnace  Current  Consumption.  —  The  current  con- 
sumed by  an  electric  furnace  per  ton  of  metal  refined  or  melted 


ELECTRIC  STEEL  203 

depends  somewhat  upon  the  kind  of  steel,  the  degree  of  refining, 
the  size  of  the  furnace,  and  the  general  operating  conditions. 
A  furnace  melting  and  refining  plain  carbon  steel  may  have  a 
current  consumption  as  low  as  450  kilowatt-hours  per  net  ton, 
whereas,  in  the  case  of  alloy  steels,  the  consumption  may  vary 
from  600  to  800  kilowatt-hours.  The  current  consumption  is 
usually  larger  for  the  smaller  installations  and  may  be  800  or 
900  kilowatt-hours  for  a  furnace  operating  on  special  steels. 
When  the  sulphur  and  phosphorus  contents  with  a  given  grade 
of  scrap  must  be  reduced  to  very  low  limits,  more  power  is  re- 
quired, because  more  slag,  made  principally  of  lime,  must  be 
melted.  Electric  furnaces  melting  cold  scrap  and  converting  it 
into  tool  or  alloy  steels  (using  two  slags)  ordinarily  have  a  cur- 
rent consumption  varying  from  700  to  800  kilowatt-hours  per 
net  ton,  whereas,  when  producing  a  merchant  grade  of  carbon 
steel  (using  one  slag),  the  consumption  may  not  exceed  from 
500  to  650  kilowatt-hours  per  ton,  the  amount  depending  upon 
the  size  of  the  furnace,  the  rapidity  of  the  melting,  and  the  grade 
of  the  scrap,  rusty  deoxidized  scrap  requiring  more  power. 
When  the  charge  is  not  melted  in  the  electric  furnace  and  the 
latter  is  used  in  conjunction  with  either  the  Bessemer  converter 
or  the  open-hearth  furnace,  the  current  consumption  is  rela- 
tively low.  For  instance,  furnaces  operating  on  the  triplex 
system  have  required  only  no  kilowatt-hours  per  ton. 


CHAPTER  X 

ROLLING    AND    DRAWING    BARS,   RAILS,   PLATES,   SHAFT- 
ING, AND   WIRE 

THE  ingots  cast  into  molds  from  the  molten  steel  made  by 
any  of  the  different  processes  described  in  the  preceding  chapters 
are  transformed  into  bars  or  sheets  by  means  of  rolling  in  a 
rolling  mill.  The  term  "rolling  mill"  is  applied  both  to  the 
machine  in  which  the  rolling  is  performed  and  to  the  plant 
where  the  rolling  operations  are  conducted.  A  rolling  mill 
plant  is  generally  so  arranged  that  the  raw  material  enters  at 
one  end  and  the  finished  material  leaves  at  the  other.  The 
rolling  mill,  in  its  narrower  sense,  may  be  defined  as  a  machine 
used  for  producing  bars  of  uniform  cross-section,  as  well  as  flat 
sheets  or  plates,  by  passing  a  short  heavy  piece  of  material,  such 
as  a  " bloom"  or  "billet,"  between  rolls  which  gradually  reduce 
it  to  the  required  form.  Final  finish  may  also  be  given  to  bars 
by  drawing  them  through  dies,  which  operation  is  known  as 
"cold  drawing"  or  "cold  rolling,"  the  latter  term  being  incor- 
rect in  that  the  operation  is  not  a  rolling  operation.  Wire  is 
produced  from  rolled  rods  by  drawing  them  through  dies  by  an 
operation  known  as  "wire  drawing." 

The  earliest  rolling  mills  were  used  in  England  in  the  latter 
part  of  the  eighteenth  century;  they  were  provided  with  plain 
grooved  rolls  for  making  round  bars.  Angles  and  T-iron  were 
later  rolled,  and,  in  1820,  the  first  rail  was  produced  by  rolling 
in  England.  Later,  the  practicability  of  rolling  plates  in  a  roll- 
ing mill  was  recognized,  the  first  plate  mill  being  built  in  Ger- 
many. The  first  I-beams  and  channels  were  rolled  in  France , 
and  the  first  segmental  shapes  used  in  older  designs  of  built-up 
columns  were  rolled  in  the  United  States.  Thus,  each  of  the 
large  industrial  nations  contributed  its  share  to  the  development 
of  the  rolling  mill  process  which  has  been  one  of  the  most  impor- 

204 


ROLLING  MILL  PRACTICE 


205 


tant  of  the  methods  used  in  connection  with  the  iron  and  steel 
industry,  and  which  has  made  possible  the  enormous  develop- 
ment of  the  use  of  iron  and  steel  for  structural  purposes. 

The  Rolling  Mill.  —  A  rolling  mill  consists  primarily  of  two 
or  more  cast-iron  or  steel  cylinders  set  one  directly  above  the 
other  in  a  frame  or  housing,  so  that  their  axes  are  parallel.  The 
rolls  are  provided  with  a  drive  so  that  they  will  rotate  in  opposite 
directions.  Rolling  mills  may  be  either  " two-high"  or  " three- 
high,"  depending  upon  whether  two  or  three  rolls  are  mounted 
one  above  the  other.  In 
the  two-high  mill,  the  ar- 
rangement of  the  rolls 
being  shown  diagramma- 
tically  at  A ,  in  Fig.  i ,  the 
bar  can  be  passed  through 
the  rolls  in  one  direction 
only,  and  is  then  passed 
back  to  the  front  of  the 
rolling  mill  by  being  passed 
over  the  top  roll,  as  indi- 
cated by  the  arrow  marked 
" return."  In  the  three- 
high  type,  the  rolls  are  so 
arranged  that  the  bar  will  pass  between  rolls  both  on  its  forward 
and  return  passage,  as  indicated  at  B,  in  Fig.  i.  It  is  evident 
that,  in  the  two-high  rolls,  the  return  passage  of  the  bar  is  an  idle 
pass,  involving  a  loss  of  time.  In  order  to  avoid  this  idle  pass, 
two-high  rolls  are  often  made  reversing,  in  which  case,  as  soon 
as  the  bar  has  passed  through  the  rolls  in  one  direction,  the  rota- 
tion of  the  roll  is  reversed  and  the  bar  is  passed  through  in  the 
opposite  direction.  The  reversal  is  controlled  either  by  a  clutch 
and  gearing  or  by  reversing  the  mill  engine.  In  the  two-high 
non-reversing  mill,  all  the  impurities  are  worked  toward  one 
end  of  the  bar,  because  the  metal  passes  through  the  mill  in  the 
same  direction  at  every  pass;  but  in  the  two-high  reversing  and 
in  the  three-high  mills,  the  impurities  are  worked  toward  the 
center  of  the  bar,  as  the  bar  is  rolled  from  each  end.  There 


Machinery 


Fig.  i.  Arrangement  of  Rolls  on  a 
"  Two-high  "  and  a  "  Three-high  " 
Rolling  Mill 


206  IRON  AND   STEEL 

is  an  advantage  in  having  the  impurities  all  worked  toward  one 
end  of  the  bar,  as  in  the  two-high  non-reversing  mill,  because 
then  that  end  of  the  bar  can  be  cut  off  and  a  better  product  is 
obtained.  The  greatest  objection  to  the  three-high  mills,  how- 
ever, is  that  the  work  must  be  raised  on  one  side  and  lowered  on 
the  other  to  make  it  enter  the  proper  grooves;  in  the  case  of  heavy 
work  this  necessitates  the  use  of  mechanical  devices.  The  revers- 
ing two-high  mills  eliminate  these  raising  devices ;  but  the  motors 
and  engines  required  for  driving  these  mills  are  so  large  and 
powerful  that  they  are  expensive  to  install;  they  are,  therefore, 
used  only  in  plants  rolling  work  that  is  difficult  to  raise  and  handle. 

In  the  early  days,  only  two-high  mills  were  used,  but,  in  order 
to  save  the  idle  time  required  for  passing  the  bar  back  over  the 
top  roll,  and  also  in  order  to  prevent  the  cooling  of  the  metal 
which  was  due  to  this  idle  pass,  the  three-high  mill  was  designed. 
As  work  is  done  on  the  metal  at  all  times,  it  does  not  have  time 
to  cool  off  between  passes,  and  the  output  of  the  plant  is  greatly 
increased. 

Each  set  of  rolls  is  arranged  in  a  housing  known  as  a  "  stand. " 
The  centers  of  the  rolls  of  each  stand  are  maintained  the  proper 
distance  apart  to  effect  a  definite  reduction  in  the  thickness 
of  the  metal  passed  between  them.  This  change  in  thickness  is, 
of  course,  accompanied  by  a  corresponding  increase  in  the  length 
of  the  bar  being  rolled. 

As  a  rule,  the  rolls  are  arranged  in  "  trains. "  These  are  formed 
by  placing  two  or  more  stands  in  a  row,  and  driving  all  of  the 
rolls  by  one  engine  or  electric  motor.  The  engine  or  motor 
drives  the  train  through  gears  which  are  connected  to  the  rolls 
by  "breaking  pieces";  similar  pieces  also  connect  the  rolls  of 
adjacent  stands.  These  " breaking  pieces"  are  spindles  that  are 
just  strong  enough  to  transmit  the  maximum  power  required  to 
drive  the  rolls.  As  a  result,  should  a  plate  or  bar  stick  while 
passing  through  the  rolls  these  pieces  will  break  and  thus  protect 
the  more  costly  rolls  from  damage.  These  breaking  pieces  are 
connected  to  the  rolls  and  the  gears  by  sleeves  that  slip  over  the 
shaped  ends  of  the  rolls,  so  that  the  connection  may  be  quickly 
made  or  broken. 


ROLLING  MILL  PRACTICE  207 

The  Rolls.  —  The  rolls  are  either  cast-iron  or  steel  cylinders, 
provided  with  grooves  for  gradually  reducing  a  heated  ingot, 
billet,  or  bloom  to  the  cross-sectional  shape  required.  When 
flat  sheets  or  plates  are  to  be  rolled,  plain  cylindrical  rolls  are 
employed.  The  rolls,  when  made  from  cast  iron,  may  be  either 
grain  rolls  or  chilled  rolls.  Grain  rolls  are  made  from  a  tough 
grade  of  cast  iron,  and  are  used  for  roughing-down  rolls.  Chilled 
rolls  are  made  from  mottled  iron  cast  in  cast-iron  molds,  which 
chill  the  surface,  making  it  very  hard.  These  rolls  are  used  for 
finishing.  Rolls  made  from  steel  castings  are  now  often  used 
for  heavy  work.  They  are  more  expensive  than  cast-iron  rolls, 
but  are  more  durable  and  may  be  made  lighter  for  equal  strength. 
They  are  especially  used  in  armor-plate  rolling  mills.  The  total 
length  of  the  roll  should  not  exceed  about  four  times  its  diameter, 
as  it  otherwise  is  liable  to  spring.  The  rolls  vary  in  size  from 
6  inches  in  diameter,  for  those  used  for  rolling  small  sizes  of 
bars,  to  50  inches  in  diameter,  for  those  used  in  making  armor 
plate. 

Definitions  of  Rolling  Mill  Terms.  —  A  "  bloom  "  is  a  square 
unfinished  piece  of  steel  which  is  about  6  inches  square  or  larger. 
A  " billet"  is  a  square  or  round  section  of  steel  which  may  be 
from  ij  inch  in  diameter  or  square  up  to  about  6  inches  in  diam- 
eter or  square.  A  "slab"  is  a  flat  piece  of  steel  at  least  2  inches 
thick  and  12  inches  wide.  A  "sheet  bar"  is  a  flat  piece  that  is 
less  than  2  inches  thick,  but  from  6  to  12  inches  wide.  By  rolling 
down  blooms,  billets,  slabs,  and  sheet  bars,  bars,  rods,  bands,  and 
hoops  are  obtained.  These  have  great  length  compared  with 
their  width  and  thickness.  A  bar  may  be  square,  round,  or  flat 
(rectangular)  in  section.  Round  and  square  bars  are  rolled  in 
sizes  of  from  T3?r  to  yi  inches,  the  sizes  from  f  to  3TV  inches  being 
standard.  Flat  bars  or  flats  are  commercially  rolled  in  sizes  of 
from  f  inch  wide  by  J  inch  thick  up  to  6  inches  wide  by  4  inches 
thick.  Flat  bars  in  sizes  from  f  inch  wide  by  J  inch  thick  to  6 
inches  wide  by  j3?-  inch  thick  are  classified  as  "light"  bars,  and 
those  i  inch  wide  by  f  inch  thick  up  to  6  inches  wide  by  4  inches 
thick  are  classified  as  "flat  bars"  and  "heavy  bands. "  The  sizes 
from  i  to  6  inches  wide  by  |  to  i  inch  thick  are  standard.  A  rod 


208  IRON  AND   STEEL 

is  generally  understood  to  be  a  round  bar.  Wire  rods  are  round 
bars  between  0.2  to  0.3  inch  in  diameter,  and  are  coiled  in  bundles. 
The  United  States  Government  limits  the  term  "wire  rod" 
to  sizes  larger  than  0.203  inch  in  diameter.  All  smaller  sizes  are 
termed  "wire."  Hoops  are  thin  flat  sections  from  f  to  8  inches 
in  width,  and  from  about  ^  to  tf\  inch  thick,  the  thickness 
generally  being  measured  by  standard  wire  gage  measurements. 
They  are  coiled  in  bundles  the  same  as  wire  rod. 

Structural  shapes  —  angles,  channels,  I-beams,  T-iron,  Z-iron, 
etc.  —  derive  their  commercial  names  from  the  shape  of  their 
cross-section.  Rails  are  subdivided  into  light  and  heavy,  light 
rails  being  those  weighing  less  than  40  pounds  per  yard.  Plates 
and  sheets  are  made  by  passing  slabs  and  sheet  bars  through 
plate  mills.  Plates  less  than  No.  10  U.  S.  plate  gage  (0.1406 
inch)  are  generally  termed  "sheets."  The  United  States 
Government  limits  the  thickness  of  sheets  to  No.  12  U.  S. 
standard  gage  (0.1094  inch).  Ordinarily,  sheet  mills  do  not  roll 
stock  thinner  than  No.  30  gage  (0.0125  inch).  Skelp  plate  is  used 
in  the  manufacture  of  tubes  and  pipes,  it  being  rolled  to  such 
width  and  thickness  as  is  required  for  the  desired  diameter  and 
strength  of  tubing.  The  edges  are  generally  sheared  for  large 
sizes  of  pipe.  Sheets  that  are  coated  with  tin  are  known  as 
"tin  plate,"  those  coated  with  a  tin-lead  alloy  are  known  as 
" terneplate, "  and  those  uncoated,  as  "black  sheets." 

The  Rolling  Process.  —  The  ingots  to  be  rolled  must  be  at 
nearly  a  white  heat  at  the  beginning  of  the  rolling  process,  and 
the  rolling  is  continued  until  the  heat  has  been  reduced  to  nearly 
a  red  heat.  In  many  plants,  the  equipment  is  such  that  a 
complete  rolling  process  from  the  ingot,  bloom,  or  billet  to  the 
finished  product  can  be  completed  in  one  heat,  but,  in  other 
cases,  the  metal  bars  are  cut  up  into  shorter  pieces,  reheated,  and 
again  rolled.  The  heating  of  the  ingots  is  done  in  furnaces, 
usually  heated  by  gas.  In  many  cases,  large  ingots  are  taken 
directly  from  the  molds  into  which  they  have  been  poured, 
as  soon  as  the  outside  has  solidified,  and  are  then  placed  in  soak- 
ing pits  or  pit  furnaces  made  of  firebrick,  in  which  they  are  kept 
until  there  is  a  uniform  heat  in  the  ingot  throughout,  so  that 


ROLLING   MILL   PRACTICE 


209 


they  can  be  properly  rolled.  The  end  of  the  ingot  of  hot  metal 
is  then  forced  between  the  rolls  and  the  metal  is  carried  forward 
by  friction.  The  reduction  in  thickness  that  can  be  made  at 
one  passage  through  the  rolls  is  comparatively  small.  Grooved 
rolls,  therefore,  are  so  made  that  a  number  of  passes  may  be 
made  through  each  stand  with  a  certain  reduction  in  size,  and 
often  some  change  in  form  in  each  pass;  but  the  number  of 
passes  that  can  be  made  for  one  heat  is  limited,  when  it  is  neces- 
sary to  roll  out  a  given  section  in  one  heat.  The  number  of 
passes  is  also  limited  by  the  fact  that  the  length  of  the  central 
part  of  the  roll  into  which  the  grooves  are  cut  should  not  exceed 
from  2\  to  3!  times  its  diameter.  As  there  is  always  a  tendency 
for  round  work  to  be  rolled  out  at  the  sides  with  each  passage 


Machinery 


Fig.  2.  Successive  Passes  for  Rolling  I-beams,  Flat  Bars,  and  T-bars 

through  the  rolls,  it  is  turned  through  an  angle  of  90  degrees, 
before  it  is  again  passed  through  the  grooves. 

The  grooves  in  the  rolls  used  for  rolling  ingots  into  rails, 
structural  shapes,  and  bars  are  dimensioned  with  great  care  in 
order  to  obtain  the  smallest  possible  number  of  passes  without 
subjecting  the  metal  to  excessive  stresses  when  rolling.  There 
are  two  classes  of  grooves,  known  as  "open"  and  "closed." 
Open  grooves  are  those  that  do  not  intermesh  in  order  to  enclose 
the  rolling  space,  as,  for  example,  the  groove  shown  to  the  left, 
at  A,  in  Fig.  2.  A  roll  with  closed  grooves  has  a  collar  that 
meshes  with  a  corresponding  groove  in  the  other  roll,  in  such  a 
way  that  the  shape  being  rolled  is  completely  enclosed  as  it 
passes  between  the  rolls.  All  the  grooves  at  A,  Fig.  2,  except  the 
one  to  the  extreme  left,  are  enclosed  grooves.  The  open  grooves 


210  IRON   AND   STEEL 

are  used  only  for  rolling  round  and  square  sections,  and  for  the 
roughing  pass  for  a  structural  shape;  for  all  other  rolling  of 
rectangular  bars,  rails,  and  structural  material,  closed  grooves 
are  used.  Fig.  2  shows  three  examples  of  successive  passes  in 
rolling;  at  At  an  I-beam;  at  B,  a  flat  bar;  and  at  C,  a  T-bar. 
In  the  case  of  the  I-beam,  two  sets  of  rolls  would  be  used  —  one 
for  the  five  passes  shown  to  the  left,  and  one  for  the  five  passes 


3.     Forty-inch  Two-high  Blooming  Mill 


shown  to  the  right.    The  first  set  of  rolls  is  known  as  the  "rough- 
ing rolls,"  and  the  second,  as  the  "finishing  rolls." 

Classification  of  Rolling  Mills.  —  Rolling  mills  are  classified 
according  to  their  product  and  the  purpose  for  which  they  are 
used.  After  an  ingot  has  reached  the  desired  temperature  in 
the  heating  furnace,  it  passes  through  the  blooming  or  slab  mill, 
which  is  used  for  reducing  ingots  to  blooms,  billets,  or  slabs. 
These  mills  reduce  the  ingot  from  a  section  which  may  be  about 


ROLLING   MILL   PRACTICE  211 

14  inches  square  to  a  section  about  6  inches  square,  so  that  it 
can  be  passed  into  the  subsequent  forming  mills.  Blooming 
mills  are  usually  of  the  two-high  reversing  type  (see  Fig.  3)  al- 
though the  three-high  non-reversing  type  is  also  employed.  The 
rolls  in  the  two-high  mills  are  from  34  to  48  inches  in  diameter, 
and  in  the  three-high  mills,  from  28  to  42  inches  in  diameter. 
The  roll-tables  of  three-high  mills,  which  support  the  stock  as  it 
passes  through  the  rolls,  are  raised  and  lowered  by  a  hydraulic 
arrangement,  so  that  the  ingot  being  rolled  is  automatically 
transferred  to  the  level  of  the  rolls  that  it  has  to  pass  through. 
Billet  mills  are  used  for  reducing  blooms  to  a  section  of  i|  inch 
square  or  larger,  so  that  these  billets  may  be  used  for  rolling 
bars  and  rods.  Billet  mills  are  generally  three-high,  with  rolls 
of  from  24  to  32  inches  in  diameter.  The  billets  are  cut  into 
certain  lengths  after  having  passed  through  the  billet  mill,  and 
the  sections  thus  obtained  are  used  for  rolling  bars  and  rods. 
Sheet-bar  mills  are  used  for  rolling  slabs  and  blooms  into  sheet- 
bars,  which  are  later  used  in  plate  mills  for  the  rolling  of  plates 
and  sheets.  These  mills  are  generally  three-high  with  rolls  of 
from  24  to  32  inches  in  diameter.  In  this  mill,  the  slabs  are  re- 
duced to  a  section  of  from  6  to  12  inches  wide  and  not  over  2 
inches  thick.  Beam  mills  are  used  for  producing  beams  and 
channels  12  inches  in  size  and  over.  They  are  generally  three- 
high  and  have  rolls  of  from  28  to  36  inches  in  diameter.  Shape 
mills  are  used  for  rolling  smaller  beams  and  channels  and  other 
structural  shapes.  They  have  rolls  of  from  20  to  26  inches  in 
diameter.  Rail  mills  are  generally  specially  designed.  They 
have  rolls  of  from  26  to  40  inches  in  diameter.  The  ends  of  the 
rails  are  trimmed  off  immediately  after  rolling  with  circular  saws; 
as  a  rule,  in  rail  mills,  these  saws  cut  three  rails  of  the  required 
length  from  one  long  rolled  rail.  Merchant-bar  mills  are  used 
for  rolling  small  sizes  of  bars  and  rods.  The  rolls  in  these  mills 
vary  from  1 6  to  20  inches  in  diameter,  for  the  larger  sizes,  down 
to  from  8  to  1 6  inches  in  diameter  in  the  smaller  sizes.  Plate 
mills  vary  in  size  from  those  making  armor  plate,  which  have 
rolls  of  from  44  to  50  inches  in  diameter  and  a  body  of  from  140 
to  1 80  inches  long,  to  sheet  mills  with  rolls  of  from  20  to  32  inches 


212  IRON   AND   STEEL 

in  diameter.  In  the  rolling  of  flat  plates,  the  horizontal  rolls 
are  adjusted  so  that  the  distance  between  them  is  reduced  after 
each  passage  of  the  sheet.  If  a  smooth,  bright  finish  is  required, 
as  on  some  sheet-steel  plates,  the  hot-rolled  sheet  is  pickled  to 
remove  the  scale  and  then  rolled  cold.  Sheets  so  treated  are 
known  as  "cold-rolled"  sheets.  When  large  tonnage  is  desired, 
billet,  sheet-bar,  rod,  sheet,  and  tube  mills  are  made  of  the 
continuous  type,  which  is  done  by  placing  a  number  of  two- 
high  stands  directly  in  front  of  one  another,  so  that  the  work 
passes  through  each  in  turn.  The  rolls  of  each  stand  are  driven 
at  different  speeds,  the  speed  increasing  as  the  work  increases  in 
length  and  approaches  completion. 

If  a  mill  is  provided  with  both  vertical  and  horizontal  rolls, 
so  that  all  four  sides  of  a  plate  may  be  rolled  simultaneously,  or 
so  that  structural  shapes  may  be  finished  completely  in  that 
manner,  they  are  known  as  universal  mills. 

Wire  Rod  Rolling.  —  Bars  of  small  diameter,  and  particu- 
larly those  intended  for  wire  drawing,  are  known  as  "wire  rod" 
and  are  rolled  in  mills  employing  a  somewhat  different  principle 
from  that  in  regular  rolling  mills.  In  the  early  development  of 
the  iron  and  steel  industry,  small  two-high,  non-reversing  mills 
with  grooved  rolls  were  used,  the  wire  rod  being  rolled  in  the 
same  manner  as  larger  bars.  Later,  the  two-high  mills  were  re- 
placed by  the  three-high  type.  At  the  present  time,  two  differ- 
ent principles  are  used  for  rod  rolling  mills,  known,  respectively, 
as  the  "Belgian"  or  "looping"  mill,  and  the  "continuous"  type 
of  mill. 

In  the  Belgian  mill,  which  owes  its  name  to  the  fact  that  the 
practice  originated  in  Belgium,  the  wire  rod  is  bent  as  it  comes 
through  the  first  rolls  and  at  once  starts  upon  its  return  pass 
between  the  upper  rolls  in  a  three-high  mill.  From  the  second 
pass,  the  wire  rod  is  bent  or  looped  back  again  into  a  third  pass, 
and  so  on.  As  the  wire  emerges  from  the  final  set  of  grooves,  it 
is  wound  on  a  reel.  Mills  of  this  type  produce  a  high  grade  of 
wire  rod,  but  the  labor  cost  is  high,  and  they  are,  therefore,  only 
used  to  a  limited  extent  in  the  United  States,  at  the  present  time. 
The  method  can  be  used  after  the  rods  have  been  reduced  to  f 


ROLLING  MILL  PRACTICE  213 

inch  in  diameter,  and  the  rod  may  pass  through  six  or  seven 
passes  in  this  way.  As  the  speed  of  the  rolls  is  the  same,  the 
rod,  due  to  the  elongation  in  the  rolling  process,  occupies  a 
larger  space  on  the  floor  between  any  two  succeeding  passes 
than  between  the  preceding  ones.  The  production  can  be  in- 
creased by  using  a  roughing  train  of  rolls  detached  from  the 
remainder  of  the  mill  and  driven  separately  at  a  lower  speed. 
It  is  considered  a  fair  production  to  turn  out  25  tons  of  wire  rod 
of  about  0.2  inch  in  diameter.  It  is  impracticable  to  roll  sec- 
tions smaller  than  this,  and  from  this  point  on,  when  smaller 
diameters  are  required,  they  are  obtained  by  wire  drawing. 

The  Belgian  mill  has  been  largely  replaced  by  the  continuous 
mill,  in  which  a  number  of  two-high  stands  are  placed  one  after 
the  other  and  close  together,  so  that  a  rod  will  pass  in  a  straight 
line  through  the  entire  mill  without  handling.  The  speed  of 
each  set  of  rolls  is  so  adjusted  that  the  wire  is  kept  taut.  In- 
stead of  turning  the  wire  at  90  degrees  between  each  passage 
through  the  rolls,  alternate  pairs  of  rolls  are  placed  in  a  vertical 
position,  in  some  continuous  mills;  but,  as  this  arrangement  has 
the  objection  of  a  high  maintenance  charge,  another  type  of  con- 
tinuous mill  was  developed  in  which  all  the  rolls  are  arranged  in 
a  horizontal  plane,  and  the  rod  turned  through  an  angle  of  90 
degrees  by  passing  it  through  guides  having  spiral  grooves  on 
the  inside  similar  to  the  rifling  of  a  gun  barrel.  Several  grooves 
may  be  cut  in  each  guide,  so  that,  as  one  set  of  grooves  becomes 
too  large  through  wear,  the  guides  may  be  shifted  to  allow  the 
rod  to  pass  through  the  next  set  of  grooves.  As  the  wire  rod 
emerges  from  the  last  stand  of  rolls,  it  is  wound  onto  a  reel. 
The  sets  of  rolls  are  placed  close  together  in  order  not  to  expose 
the  hot  metal  to  the  air  more  than  is  necessary.  In  the  contin- 
uous process  of  wire  rod  rolling,  it  is  possible  for  one  end  of  the 
billet  to  be  in  the  furnace  while  part  of  it  passes  through  the  mill 
and  the  other  end  is  wound  upon  a  reel.  The  production  has 
been  increased  many  times  as  compared  with  the  Belgian  mill, 
400  tons  per  day  being  possible  with  one  continuous  mill  when  a 
continuous  furnace  is  used.  This  furnace  is  automatically 
charged  and  discharges  the  hot  billets  into  the  roughing  mill 


214  IRON   AND    STEEL 

directly  in  front  of  the  furnace  door.  A  combination  of  the 
looping  mill  and  the  continuous  mill  has  also  been  made.  A 
continuous  roughing  mill  is  used  for  breaking  down  a  billet  to 
looping  sizes,  and  then  a  looping  mill  is  employed  for  rolling  the 
wire  to  the  smaller  size. 

Making  Cold-drawn  Shafting.  —  The  terms  " cold-drawn"  and 
" cold-rolled"  are  indiscriminately  applied  to  all  grades  of  shaft- 
ing and  screw  stock  with  a  bright  finish;  but  these  two  processes 
are  entirely  distinct.  Cold-drawn  shafting  and  screw  stock  are 
made  by  drawing  the  steel  bar  through  a  die,  which  reduces  the 
diameter  to  exactly  the  required  size  and  imparts  a  high  finish 
to  the  surface  of  the  metal;  and  cold-rolled  shafting  is  made  by 
turning  the  bar  to  just  about  the  required  diameter  and  then 
obtaining  the  final  reduction  and  finish  by  passing  it  through  a 
machine  equipped  with  burnishing  rolls.  It  will  be  evident 
from  this  that  the  rolling  process  is  very  different  from  the 
method  of  treatment  to  which  steel  is  subjected  when  it  is  rolled 
hot  to  reduce  the  diameter  and  increase  the  length  of  the  bar. 
Either  cold-drawing  or  cold-rolling  imparts  a  hard  surface  to 
the  steel  and  increases  the  tensile  strength  of  the  bar.  In 
addition  to  cold-drawing  and  cold-rolling,  there  is  a  third  method 
which  finds  general  application  in  the  production  of  shafting  over 
three  inches  in  diameter;  this  consists  of  simply  turning  the  bar 
down  to  the  required  diameter,  taking  particular  care  to  take  a 
light  finishing  cut  that  will  leave  the  surface  as  smooth  and  uni- 
form as  possible.  Most  shafting  and  screw  stock  up  to  three 
inches  in  diameter  is  cold-drawn,  and  shafting  above  that  size 
is  generally  turned. 

Steel  for  Making  Cold-drawn  Shafting.  —  Cold-drawn  shaft- 
ing is  made  from  an  open-hearth  steel  containing  about  0.15  per 
cent  of  carbon,  which  is  similar  to  the  grade  commonly  known 
as  "machinery"  steel.  In  most  plants  engaged  in  the  manufac- 
ture of  cold-drawn  shafting,  the  raw  material  is  purchased  from 
the  steel  mill  in  the  form  of  bars  having  a  diameter  from  J3  to  J 
inch  larger  than  the  shafting  to  be  drawn,  the  amount  of  excess 
metal  increasing  with  the  size  of  the  work;  but  as  the  produc- 
tion of  this  raw  material  is  an  important  part  of  the  shafting 


COLD-DRAWING  215 

industry,  a  brief  description  of  the  method  employed  will  be 
given. 

Molten  steel,  which  has  been  brought  to  the  required  chemical 
composition  by  refining  in  an  open-hearth  furnace,  is  poured 
into  ingot  molds  that  produce  ingots  ranging  from  16  to  20 
inches  square  by  from  4  to  5  feet  in  length,  weighing  approxi- 
mately from  3200  to  6250  pounds.  These  are  the  regular  steel 
works  ingots  that  might  ultimately  be  worked  up  into  a  variety 
of  other  products  in  addition  to  cold-rolled  shafting.  After 
being  removed  from  the  mold,  the  ingots  are  transferred  to  a 
blooming  mill,  in  which  they  are  rolled  down  into  billets  of  from 
2  to  5  inches  square,  according  to  the  size  of  the  shafting  to  be 
made. 

The  next  step  in  the  process  will  depend  upon  the  kind  of 
shafting  that  is  to  be  produced;  but  in  any  case  the  billets  pro- 
duced in  the  blooming  mill  are  cut  up  into  pieces  of  such  a  length 
that  they  can  be  rolled  out  into  bars  of  the  same  length  as  the 
shafting  to  be  drawn.  In  most  cases,  the  length  of  billet  is  such 
that  the  rolled  bars  will  be  from  30  to  40  feet  in  length,  as  this  is 
the  greatest  length  that  can  be  handled  in  an  ordinary  freight 
car.  The  billets  are  reheated  and  then  rolled  down  into  bars 
of  this  length,  of  a  diameter  slightly  larger  than  the  required 
size  of  the  shafting. 

Pickling  Hot-rolled  Bars.  —  The  steel  bars  that  the  shafting 
factory  purchases  from  the  steel  mill  have  been  rolled  hot,  and 
as  a  result  they  are  covered  with  an  oxide  scale,  which  must 
be  removed  before  the  bars  can  be  converted  into  cold-drawn 
shafting.  The  reason  for  this  is  that  the  oxide  scale  is  extremely 
hard  and  would  rapidly  destroy  the  drawing  dies;  also,  cold- 
drawn  shafting  is  required  to  have  what  is  known  as  a  "bright'' 
finish,  and  this  can  only  be  obtained  when  the  metal  is  free  from 
oxide.  Another  reason  for  removing  every  particle  of  scale 
from  the  bars  before  they  are  drawn  is  that,  if  it  were  not  re- 
moved, small  pieces  of  scale  would  be  driven  into  the  steel  by 
the  die  pressure  and  cause  flaws  that  would  seriously  reduce  its 
strength.  The  first  step  in  cleaning  or  " pickling"  the  metal  is 
to  place  the  bars  of  steel  in  wooden  troughs  containing  a  5-per- 


2l6  IRON  AND    STEEL 

cent  solution  of  commercial  sulphuric  acid,  which  was  a  specific 
gravity  of  66  degrees  Baume  at  a  temperature  of  60  degrees  F. 
The  scale  is  removed  by  a  combined  chemical  and  mechanical 
action;  the  acid  reacts  with  the  iron  and  liberates  hydrogen, 
which  collects  under  the  oxide  scale  and  develops  sufficient 
pressure  to  tear  away  the  scale  in  small  plates.  As  the  chemical 
action  is  accelerated  by  heat,  the  temperature  of  the  acid  bath 
is  raised  to  about  180  or  200  degrees  F.  by  means  of  pipes  which 
deliver  live  steam  into  the  trough. 

The  shafting  must  be  left  in  the  acid  bath  only  long  enough 
to  remove  the  scale,  as  otherwise  the  steel  would  be  eaten  away 
and  the  diameter  of  the  bars  reduced  so  that  they  would  be  too 
small  for  making  shafting  of  the  size  for  which  they  are  intended. 
It  is  particularly  important  to  regulate  the  length  of  time  the 
steel  is  left  in  the  acid  bath  in  the  case  of  high-carbon  steel,  as 
experience  has  shown  that  the  acid  tends  to  decarbonize  the  steel 
at  the  surface.  Low-carbon  steel  can  be  left  in  the  bath  for  from 
12  to  15  minutes,  and  sometimes  20  minutes  will  not  be  too  long; 
but  high-carbon  steel  must  not  be  exposed  for  more  than  4  or  5 
minutes.  After  being  removed  from  the  acid  bath,  the  steel 
bars  are  rinsed  in  troughs  containing  pure  water,  after  which 
they  are  transferred  to  troughs  containing  a  solution  of  lime- 
water,  which  has  the  property  of  neutralizing  the  acid  and  pre- 
venting further  action  of  any  slight  trace  of  acid  that  may  still 
adhere  to  the  bars.  The  dipping  of  the  bars  in  lime  water  also 
has  a  further  valuable  purpose;  when  removed  from  the  bath, 
the  bars  are  covered  with  a  solution  of  limewater,  and  after  the 
water  has  dried  off,  this  solution  leaves  a  deposit  of  lime  which 
protects  the  steel  from  oxidation  by  the  oxygen  in  the  atmos- 
phere. In  order  to  prevent  the  steel  from  rusting,  it  is  of  the 
highest  importance  that  the  bars  be  dried  quickly  after  they  are 
removed  from  the  limewater  bath. 

Pointing  Bars  preparatory  to  Drawing.  —  Before  the  cleaned 
steel  bars  can  be  subjected  to  the  cold-drawing  operation,  it  is 
necessary  for  them  to  be  pointed  at  one  end  so  that  the  point 
can  be  passed  through  the  drawing  die  and  gripped  by  the  tongs 
of  the  draw-bench.  The  method  of  pointing  varies  according  to 


COLD-DRAWING  217 

the  size  of  the  bars  that  have  to  be  drawn,  and  practice  in  this 
connection  also  varies  according  to  the  shop  in  which  the  work 
is  done.  In  general,  bars  of  the  larger  sizes  are  pointed  in  a 
machine  equipped  with  a  cutter-head  that  actually  removes 
metal  from  the  end  of  the  bar.  On  smaller  sized  bars,  the 
pointing  is  done  in  a  swaging  or  rolling  machine  which  hammers 
or  rolls  down  the  end  of  the  bar. 

Pointing  round  bars  ready  for  the  cold-drawing  operation  is 
a  simple  matter,  because  the  shape  of  the  work  offers  no  par- 
ticular difficulty;  but  it  is  necessary  for  the  shape  of  the  point 
to  be  the  same  as  that  of  the  bar  which  is  to  be  drawn,  so  that, 
in  the  case  of  square,  hexagon,  flat,  and  V-shaped  bars,  the 
point  must  be  of  the  same  shape  as  the  finished  bar.  In  order 
to  secure  this  result  special  methods  must  be  employed.  One 
of  the  most  satisfactory  processes  consists  of  heating  the  end  of 
the  bar  and  then  gripping  it  on  each  side  of  the  heated  section 
by  clamps  on  a  machine  which  provides  for  pulling  the  bar 
sufficiently  to  "neck  in"  the  heated  section  and  point  it.  Those 
who  have  conducted  tests  on  a  testing  machine  will  recall  that, 
in  stretching  hexagon  and  other  shaped  sections,  the  neck 
produced  holds  the  shape  of  the  original  bar.  Where  this  method 
is  employed  for  pointing  bars  ready  for  drawing,  it  is  important 
not  to  exceed  the  elastic  limit  of  the  material,  as  such  a  con- 
dition would  result  in  a  rapid  reduction  of  diameter.  To  over- 
come this  condition,  the  operator  of  the  machine  has  a  sponge 
soaked  in  water,  and  as  soon  as  he  notices  any  tendency  for  the 
diameter  of  the  bar  to  reduce  rapidly  at  some  point,  he  drops  a 
little  water  on  the  metal  so  that  the  temperature  is  lowered  and 
the  metal  hardens  sufficiently  to  prevent  further  reduction  in 
diameter  at  the  point  where  the  elastic  limit  has  been  exceeded. 

Starting  the  Bar  through  the  Die.  —  The  carriage  on  a  draw- 
bench  is  furnished  with  two  serrated  jaws  that  grip  the  work. 
These  jaws  are  tapered  on  the  outside  and  fit  into  a  tapered 
holder  on  the  carriage;  the  result  is  that,  when  the  jaws  are 
pressed  against  the  work  and  the  carriage  starts  forward,  they 
are  drawn  back  in  their  tapered  holder,  which  forces  them  to 
secure  a  firm  grip  on  the  work.  For  drawing  stock  over  one  inch 

I4  F 


2l8 


IRON  AND   STEEL 


COLD-DRAWING  2lp 

in  diameter,  some  manufacturers  have  their  draw-benches 
equipped  with  an  auxiliary  carriage  located  behind  the  die- 
holder  (see  Fig.  4) ,  which  is  fitted  with  a  pair  of  tapered  serrated 
jaws  that  can  grip  the  work.  Attached  to  this  carriage  is  a 
yoke  that  drops  over  the  die-holder  so  that  a  bar  at  the  front  end 
of  the  yoke  may  be  gripped  by  the  jaws  of  the  regular  draw- 
bench  carriage.  When  the  main  carriage  is  started,  this  yoke 
draws  the  auxiliary  carriage  forward,  which  results  in  push- 
ing the  front  end  of  the  bar  of  steel  through  the  die.  Fig.  5 


Fig.  5.     View  of  Die  from  Front  after  End  of  Bar  has  been  pushed 

shows  the  apparatus  on  another  draw-bench  after  the  bar  has 
been  pushed  through  the  die  and  the  yoke  released  from  the 
jaws  of  the  main  carriage  and  raised  by  means  of  the  cable  and 
counterweight  furnished  for  that  purpose.  The  operator  will 
now  draw  the  main  carriage  back  and  grip  the  projecting  end  of 
the  bar  between  its  jaws;  he  will  then  release  the  jaws  of  the 
auxiliary  carriage  from  the  work  and  start  the  draw-bench,  to 
pull  the  bar  through  the  die.  This  is  the  means  of  saving  the 
crop  end  of  steel,  which  results  through  the  customary  practice 
of  pointing  the  end  of  the  bar  so  that  it  may  be  threaded  through 
the  die.  On  bars  less  than  one  inch  in  diameter,  this  method 


220 


IRON'  AND   STEEL 


cannot  be  used,  because  the  bar  buckles  instead  of  being  pushed 
through  the  die. 

Types  of  Draw-benches  Used.  —  Two  types  of  machines  are 
generally  used  for  drawing  shafting  and  screw  stock.  The 
first  of  these  is  known  as  the  " straight  draw-bench"  (see  Fig. 
6),  on  which  a  straight  rod  (and  sometimes  more  than  one  rod) 
is  drawn  through  the  die  by  means  of  tongs  on  a  head  which 
travels  along  a  straight  line  on  the  draw-bench,  power  being 
furnished  by  an  endless  sprocket  chain  or  by  hydraulic  pres- 


Fig.  6.     Straight  Draw-bench  pulMng  Four  Rods  Simultaneously 

sure.  The  second  type  is  the  bull-block  or  rotary  machine  (see 
Fig.  7)  on  which  the  rod  is  in  the  form  of  a  coil  that  is  carried 
on  a  reel  at  one  end  of  the  machine;  the  end  of  this  rod  is 
pointed  and  threaded  through  the  drawing  die  and  gripped  by 
tongs  carried  on  a  second  reel,  which  rotates  in  such  a  way  that 
the  rod  is  drawn  through  the  die  and  wound  up  on  the  second 
reel.  Both  types  of  machines  have  points  in  their  favor. 

The  straight  draw-bench  is  generally  used  for  shaftings  and 
rods  from  f  inch  in  diameter  and  up;  the  most  obvious  advan- 
tage claimed  for  it  is  that  the  material  is  always  straight,  and 
consequently  requires  little  treatment  after  the  drawing  opera- 


COLD-DRAWING  221 

tion  has  been  completed.  The  bull-block  machine  winds  up  the 
cold-drawn  steel  in  a  coil,  which  must  be  carefully  straightened 
to  prepare  it  for  use.  This  takes  time  and  involves  an  additional 
item  of  expense  in  the  process  of  manufacture;  but  there  are  a 
number  of  factors  in  the  bull-block  machine  that  offset  this 
expense,  if  they  do  not  actually  introduce  a  material  factor  of 
saving.  In  the  first  place,  the  material  in  coils  is  much  more 
convenient  to  transport  through  the  plant,  as  the  stock  can  be 
carried  on  trucks  and  the  plant  does  not  have  to  be  laid  out  in 
such  a  way  that  long  bars  can  be  handled  conveniently.  In  the 
second  place,  it  is  possible  to  draw  coils  of  steel  weighing  from 
300  to  400  pounds  and  containing  anywhere  from  $00  to  600 
feet  of  rod,  according  to  the  diameter;  consequently  the  cost  of 
production  is  much  less  because  the  number  of  crop  ends  and 
the  amount  of  scrap  metal  are  greatly  reduced.  In  fact,  this 
is  the  most  important  claim  made  for  the  bull-block  machine. 
The  rate  of  production  is  also  higher,  because  the  time  spent  in 
setting  up  the  machine  is  less  where  these  long  coils  can  be  drawn 
at  one  continuous  operation.  Practice  varies  in  different  plants, 
but  as  a  general  rule  straight  draw-benches  are  used  for  handling 
stock  from  %  inch  in  diameter  and  up,  while  bull-block  machines 
are  used  for  stock  up  to  J  inch.  However,  there  are  a  number  of 
cases  in  which  bull-block  machines  have  been  successfully  em- 
ployed for  drawing  bars  up  to  |  inch  in  diameter.  Squares, 
rectangles,  hexagons,  octagons,  and  other  irregular  shapes  are 
being  drawn  on  bull-blocks  in  addition  to  round  stock. 

Where  the  attempt  is  made  to  draw  stock  larger  than  f  inch 
in  diameter,  trouble  has  sometimes  been  experienced  through 
the  tendency  for  the  cross-section  to  be  slightly  distorted.  For 
instance,  in  round  stock  the  tendency  is  for  the  cross-section 
to  become  slightly  elliptical.  This  is  due  to  the  fact  that  the 
material  is  being  coiled  on  a  comparatively  small  drum,  and 
trouble  of  this  kind  is  especially  likely  to  happen  when  low- 
carbon  steel  is  being  drawn.  Sometimes  it  has  been  found 
possible  to  compensate  for  this  in  the  shape  of  the  die  or  by  em- 
ploying special  methods  of  straightening  the  stock.  There  is  a 
wide  difference  of  opinion,  however,  as  regards  the  maximum 


222 


IRON  AND   STEEL 


COLD-DRAWING  223 

the  right-hand  end  of  the  bench  is  not  in  operation,  although 
it  is  in  position  to  be  threaded  up  ready  to  start  work.  Just  at 
the  right  of  this  block  and  projecting  up  through  the  bench 
there  is  a  lever  B  which  is  so  arranged  that  if  a  man  is  caught  by 
the  wire  between  the  die  and  the  block,  while  feeling  the  wire 
to  see  if  the  die  is  working  properly,  his  body  is  drawn  up  on  the 
bench  and  strikes  this  lever,  which  automatically  stops  the  block 
rotating  and  prevents  a  serious  accident.  Accidents  of  this 
kind  are  by  no  means  uncommon  among  wire  mill  operators, 
and  unless  means  are  provided  for  stopping  the  machines  the 
accident  is  likely  to  be  a  severe  one.  At  the  front  of  the  die- 
stand  or  die-holder  there  will  be  seen  a  guard  ring  C,  which  is  a 
further  device  to  provide  for  the  operator's  safety.  In  case  he  is 
caught  by  the  wire  between  the  reel-stand  which  holds  the  coil 
of  steel  and  the  die,  his  body  is  drawn  up  against  this  guard  ring, 
which  automatically  operates  an  air  valve  that'  stops  the  bull- 
block  from  rotating. 

On  top  of  block  A  at  the  right-hand  side  there  will  be  seen 
what  are  known  as  " pullers"  D  hanging  down  at  the  side  of  the 
block.  These  are  drawn  forward  with  the  right  hand  and  at- 
tached to  the  point  of  the  steel  that  projects  through  the  die, 
after  which  the  block  is  ready  to  be  started  rotating  to  draw  the 
steel  through  the  die  and  wind  it  up  on  block  A.  Between 
blocks  A  and  £  is  a  pointing  machine  F,  which  is  used  for  pointing 
the  end  of  a  coil  of  steel  so  that  it  may  be  threaded  through  the 
die  to  be  gripped  by  the  pullers.  This  pointing  machine  is 
driven  by  a  chain  drive  from  the  lineshaf t  and  is  of  the  continuous 
type,  i.e.,  the  pointing  rollers  always  run  in  the  same  direction 
instead  of  oscillating  as  they  do  in  another  type  of  machine  for 
pointing  stock.  In  the  rollers  there  are  cut  grooves,  the  cross- 
section  of  which  is  gradually  reduced  so  that,  as  the  wire  is 
drawn  through,  its  diameter  is  reduced  sufficiently  so  that  the 
point  may  be  threaded  through  the  die  in  the  manner  described. 

Bull-block  E  is  shown  after  the  wire  has  been  finally  drawn 
through  the  die  and  the  bundle  has  been  partially  stripped  off 
the  block.  Block  G  has  a  wire  threaded  up  through  the  die  and 
the  block  is  ready  to  start  making  the  draft.  Block  H  is  shown 


224  IRON  AND   STEEL 

engaged  in  the  operation  of  drawing  wire,  and  is  partially  cov- 
ered with  drawn  wire.  Blocks  /  and  /  are  not  shown  in  any 
special  positions. 

After  the  drawing  operation  has  been  started,  the  wire  is 
gaged  to  see  that  it  is  true  to  size;  and  when  the  operator  of 
the  draw-bench  is  satisfied  that  this  is  the  case,  he  starts  the  bull- 
block  again  and  draws  all  the  wire  through  the  die.  After  the 
steel  has  been  drawn  through  the  die,  it  is  ready  for  the  market 
as  soon  as  the  pointed  end  has  been  cropped  off  and  the  bundle 
of  wire  has  been  gaged  at  both  ends  to  see  that  the  variation  in 
size  between  the  two  ends  is  within  the  required  limit  of  accuracy. 
In  both  cold-drawn  shafting  and  cold-drawn  wire,  this  limit  will 
not  exceed  0.0005  mcn  ^  the  work  is  properly  done.  Some 
variation  is  bound  to  exist  due  to  wear  of  the  die,  and  the  amount 
of  error  will  usually  depend  upon  the  quality  of  the  die  and  the 
care  with  which  the  steel  and  die  are  lubricated  during  the  draw- 
ing operation.  Other  factors  that  affect  the  degree  of  accuracy 
obtained  are  the  amount  of  reduction  required  from  the  rod  to 
the  finished  steel,  quality  of  the  steel,  care  taken  in  the  pickling 
operation,  and  care  taken  in  drying  the  stock  after  it  has  been 
immersed  in  the  lime  bath. 

Speeds  at  which  Cold-drawing  is  done.  —  The  speed  at  which 
cold-drawn  steel  stock  or  shafting  is  pulled  through  the  die 
varies  considerably  with  the  size  of  the  stock  being  drawn.  The 
larger  the  diameter,  the  lower  must  be  the  rate  at  which  it  is 
drawn  through  the  die.  Bull-blocks  or  draw-benches  are  not 
arranged  to  give  a  variable  speed,  but  the  gearing  and  diameter 
of  the  blocks  on  a  bench  may  be  varied,  thereby  accomplishing 
the  same  results.  Most  steel  mills  drive  their  blocks  with  elec- 
tric motors,  a  motor  driving  from  one  or  two  blocks  up  to  any 
number  within  the  range  of  its  capacity.  The  actual  drawing 
speed  varies  from  250  to  375  feet  per  minute,  according  to  the 
diameter  of  the  wire  and  the  character  of  the  steel  being  drawn. 
The  following  represents  the  practice  of  the  Pennsylvania  Shaft- 
ing Co.,  Spring  City,  Pa.,  in  drawing  steel  shafting  on  straight 
draw-benches.  On  a  bench  handling  four  bars  at  once  (see  Fig. 
6),  ranging  from  yV  to  i  inch  in  diameter,  the  speed  at  which  the 


COLD-DRAWING  225 

steel  is  drawn  through  the  dies  is  16  feet  per  minute.  For  stock 
from  iyV  to  2  inches  in  diameter,  drawing  one  bar  at  a  time,  the 
speed  is  1 6  feet  per  minute.  When  drawing  steel  from  2  inches 
in  diameter  to  3!  inches,  with  one  bar  drawn  at  a  time,  the  speed 
is  8  feet  per  minute.  In  the  case  of  flat  bars  ranging  in  size 
from  I  by  5  to  i  by  5  inches,  and  hexagons  of  about  the  same 
cross-sectional  area,  the  speed  of  drawing  is  n  feet  per  minute. 
In  drawing  bars  from  i  to  i|  inch  square  or  f  by  if  inch  flat,  a 
drawing  speed  of  16  feet  per  minute  will  give  satisfactory  results. 
Reduction  of  Stock  by  Cold-drawing.  —  In  conducting  the 
cold-drawing  operation,  the  entire  reduction  is  obtained  by  one 
passage  of  the  steel  through  the  drawing  die.  The  amount  of 
reduction  obtained  varies  according  to  the  diameter  of  the 
shafting  which  is  being  drawn,  but  for  sizes  J  inch  in  diameter  and 
over,  a  reduction  of  TTF  inch  may  be  obtained;  and  for  smaller 
sizes  of  shafting,  the  reduction  is  about  ^  inch.  In  drawing  some 
large  sizes  of  shafting,  a  reduction  as  high  as  \  inch  is  obtained. 
The'  bars  of  steel  ordered  from  the  rolling  mill  are  specified  to 
have  a  diameter  which  exceeds  that  of  the  shafting  to  be  produced 
by  the  amount  of  reduction  which  may  be  obtained  by  one  pas- 
sage through  the  drawing  die.  The  reductions  referred  to  are 
for  steel  containing  0.15  per  cent  of  carbon;  for  high-carbon  steel 
used  in  the  manufacture  of  drill  rod  and  certain  other  products, 
the  amount  of  reduction  possible  by  one  passage  through  the 
dies  is  much  less,  as  it  is  found  that  where  the  reduction  is  too 
great  there  is  a  tendency  for  the  fibers  of  the  metal  to  break  and 
thus  cause  a  serious  reduction  in  the  strength  of  the  bars;  con- 
sequently, the  drawing  of  drill  rod  is  conducted  in  such  a  way 
that  a  number  of  reductions  are  obtained  by  successive  passages 
of  the  steel  through  the  drawing  dies  until  the  diameter  of  the 
bar  has  been  reduced  to  exactly  the  required  size.  For  bars  up 
to  J  inch  in  diameter,  the  amount  of  reduction  at  one  draft  is 
7V  inch;  for  bars  from  T\  to  3  inches  in  diameter,  the  amount 
of  reduction  per  draft  is  TV  inch;  and  for  bars  from  3TV  up  to 
6  inches  in  diameter,  the  amount  of  reduction  per  draft  is  | 
inch.  Bars  over  3  inches  in  diameter  can  be  most  profitably 
finished  by  turning.  The  heavier  the  draft  the  smoother  and 


226  IRON  AND    STEEL 

cleaner  the  surface  of  the  cold-drawn  steel;  but  extremely  heavy 
drafts  require  more  power,  and  in  the  case  of  alloy  steels  or 
steels  containing  a  high  percentage  of  carbon,  such  heavy  drafts 
may  disturb  the  structure  of  the  steel  and  make  it  unsuitable  for 
the  desired  use,  although  a  superior  finish  is  obtained. 

Advantages  of  Cold-drawing  Process.  —  Two  important  ad- 
vantages are  secured  from  the  process  of  cold-drawing:  First, 
the  metal  does  not  oxidize,  because  the  work  is  done  cold,  and 
as  a  result  the  steel  retains  a  so-called  " bright"  finish.  Second, 
it  is  possible  to  hold  the  material  within  very  close  limits,  the 
diameter  of  good  cold-rolled  shafting  or  screw  stock  being  within 
0.0005  inch  of  the  specified  diameter.  The  clean  and  extremely 
smooth  finish  produced  in  this  way  enables  a  high  transmission 
efficiency  to  be  obtained  with  cold-drawn  shafting,  as  friction 
losses  in  bearings  are  reduced  to  a  minimum.  Advantage  is 
taken  of  this  method  in  producing  material  used  for  various  other 
purposes,  such  as  the  manufacture  of  parts  in  automatic  screw 
machines,  etc.,  as  it  is  found  that  the  smooth  finish  and  uniform 
diameter  of  cold-rolled  drawn  bars  enable  them  to  be  handled  by 
automatic  machinery  with  much  better  results;  and  advantages 
may  also  be  taken  of  the  high  finish  of  the  bar  to  avoid  the 
necessity  of  further  machining  of  surfaces  where  the  original 
diameter  of  the  bar  meets  all  requirements.  In  this  way  a  con- 
siderable saving  is  made  in  both  material  and  production  time. 

Dies  Used  for  Drawing  Small  Stock.  —  There  are  two  general 
classes  of  dies  used  for  drawing  screw  stock.  These  are,  first,  the 
chilled  cast-iron  die,  and,  second,  the  so-called  " steel  die-plate." 
Cast-iron  dies  are  made  with  one  opening  for  drawing  a  specified 
size  of  steel,  while  in  the  die-plates  there  are  a  number  of  open- 
ings, which  are  used  in  succession  until  all  have  been  worn  over 
size.  Although  the  method  of  drawing  steel  through  these  types 
of  dies  is  the  same,  the  practice  in  maintaining  the  dies  in  proper 
condition  for  use  is  quite  different.  In  drawing  steel  through 
either  type  of  die,  it  will  be  obvious  that  friction  gradually 
wears  the  die  over  size,  and  when  the  limit  of  over  size  for  drawing 
a  given  diameter  of  steel  has  been  reached,  the  methods  of  put- 
ting the  two  types  of  dies  into  condition  for  further  use  are 


COLD-DRAWING  227 

quite  different.  In  the  case  of  a  cast-iron  die  that  has  reached 
the  limit  of  over  size  allowable,  the  method  of  procedure  is  to 
remove  the  die  from  the  draw-bench  and  ream  out  the  hole  to 
the  minimum  diameter  allowable  for  drawing  the  next  larger 
size  of  steel  made  in  the  mill  where  this  die  is  used. 

With  steel  die-plates  an  entirely  different  procedure  is  fol- 
lowed. The  die-plate  is  heated  and  hammered  on  the  "leaving" 
or  back  side  of  the  die,  so  that  the  steel  is  forced  inward  around 
the  hole,  reducing  its  diameter  slightly  more  than  the  required 
amount.  It  then  goes  to  a  man  known  as  a  " plate  setter"  who 
uses  a  tapered  punch  which  he  hammers  into  the  hole  in  the  die 
while  the  metal  is  cold,  thus  compressing  the  steel  around  the 
hole  and  at  the  same  time  enlarging  the  hole  to  the  minimum 
diameter  which  is  allowed  for  drawing  a  given  size  of  steel. 
Steel  die-plates  were  once  used  almost  exclusively  in  the  United 
States  for  drawing  steel  wire  and  small  sizes  of  screw  stock,  but 
at  the  present  time  cast-iron  dies  are  more  extensively  employed 
for  drawing  round  wire.  For  shapes  other  than  rounds,  i.e., 
ovals,  half  rounds,  squares,  hexagons,  etc.,  it  is  probable  that 
steel  die-plates  will  continue  to  be  used  because  of  the  difficulty 
that  would  be  experienced  in  maintaining  cast-iron  dies  in  suit- 
able condition  for  operation.  This  is,  of  course,  due  to  the 
fact  that  irregular-shaped  die  openings  cannot  be  reamed.  In 
Europe  and  especially  in  English  wire  mills,  steel  die-plates  are 
still  generally  used. 

Although  steel  plates  can  be  used  repeatedly  for  drawing  wire 
of  the  same  sized  hole,  while  cast-iron  plates  have  to  be  reamed 
out  for  a  new  size  of  wire  each  time  they  are  used,  the  original 
cost  of  the  steel  plates  and  the  labor  expense  involved  in  setting 
them  back  for  drawing  the  same  size  wire  are  greatly  in  excess  of 
the  cost  of  the  cast-iron  die  and  the  labor  charge  involved  in 
reaming  it  out  to  permit  a  larger  size  wire  to  be  drawn.  Chilled 
cast-iron  dies  and  steel  die-plates  are  usually  made  for  drawing 
stock  up  to  J  inch  in  diameter;  in  some  cases,  larger  stock  is 
drawn  in  these  dies. 

Dies  for  Drawing  Shafting  and  Larger  Sizes  of  Screw  Stock. 
—  For  drawing  the  larger  sizes  of  screw  stock  and  all  sizes  of 


228 


IRON   AND   STEEL 


shafting,  there  are  several  types  of  dies  that  are  commonly 
employed.  For  drawing  round  stock,  the  most  commonly  used 
die  consists  of  a  disk  of  high-speed  steel  with  a  round  opening 
which  is  bell-mouthed,  tapering  gradually  down  to  a  straight 
throat  of  the  same  diameter  as  that  of  the  steel  which  it  is  desired 
to  draw. 

There  are  two  types  of  drawing  dies  in  general  use  which  are 
known  as  the  "hard"  die  and  the  ".soft"  die.  As  their  names 
imply,  the  steel  in  these  two  types  is  hardened  or  left  soft  as  the 


1  —  1 

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Machinery 


Fig.  8.     Front  and  Cross-sectional  Views  of  So-called  "Turk's 
Head"  or  Combination  Die 

case  may  be,  and  each  form  has  certain  points  in  its  favor.  The 
hard  die  is  made  to  exactly  the  required  form  and  size,  after 
which  it  is  heated  and  quenched  by  passing  a  stream  of  cold 
water  through  the  opening.  This  results  in  hardening  the  metal 
so  that  the  die  is  able  to  draw  from  500  to  1500  40-foot  bars 
according  to  the  nature  of  the  steel  in  the  bars  and  in  the  dies 
through  which  they  are  drawn.  Soft  dies  have  a  capacity  for 
drawing  only  from  12  to  15  4o-foot  bars,  but  they  are  easily 
put  back  into  condition  for  further  service.  This  is  done  by 
hammering  the  dies  at  the  "leaving"  side,  which  results  in 


COLD-DRAWING 


229 


causing  the  metal  to  flow  in  and  reduce  the  diameter  of  the 
opening,  after  which  the  hole  is  reamed  out  to  exactly  the  re- 
quired size.  This  work  can  be  done  rapidly. 

In  the  case  of  the  hard  die,  it  is  necessary  to  heat  it  above  the 
critical  temperature  and  then  pass  a  stream  of  cold  water  through 
the  opening,  which  causes  the  inner  part  to  shrink  sufficiently  to 
draw  in  the  hot  outer  section,  thus  reducing  the  diameter  of  the 
hole  beyond  the  required  size,  after  which  the  die  is  lapped  out 
to  secure  the  correct  diameter.  This  is  necessarily  a  slow  and 
costly  operation,  so  that, 
although  the  hard  die  has 
a  far  greater  capacity  as 
regards  its  productive  life, 
the  cost  of  putting  it  back 
into  condition  after  it  is 
worn  out  is  much  greater 
than  in  the  case  of  the 
soft  die. 

Dies  used  for  Drawing 
Squares,  Rectangles,  and 
Irregular  Shapes.- 
Different  methods  must 
be  followed  in  designing 
dies  for  drawing  square  and  irregular-shaped  bars  from  those  used 
in  making  dies  for  round  stock,  because  trouble  would  be  experi- 
enced in  maintaining  solid  dies  of  these  shapes  in  the  required 
condition.  Some  dies  for  drawing  squares,  hexagons,  and  octagons 
are  made  from  solid  blocks,  but  it  is  probably  better  practice  to 
use  either  a  die  of  the  type  known  as  a  "Turk's  head"  or  one  of 
the  special  dies  constructed  with  rollers  that  engage  the  stock  to 
be  drawn.  Fig.  8  shows  the  Turk's  head  type  of  die,  and  Figs.  9 
and  10  show  front  and  rear  views  of  one  of  the  rolling  type  of  dies. 

The  Turk's  head  die  has  a  steel  frame  in  which  are  supported 
two  pieces  A,  known  as  "distance  pieces,"  and  two  side  pieces 
B.  These  four  parts  are  securely  wedged  in  place  in  the  frame, 
so  that  the  die  opening  is  kept  the  desired  size.  Compensation 
for  wear  of  the  die  is  made  by  adjusting  the  position  of  the  side 


Fig.  9.     Roller  Die  built  by  Standard 
Machinery  Co.  for  Drawing  Square  Bars 


230 


IRON  AND   STEEL 


pieces  and  distance  pieces  with  wedges  in  the  die  frame.  The 
distance  pieces  and  side  pieces  are  fitted  together  in  such  a  way 
that  the  pressure  applied  in  drawing  the  steel  through  the  die 
cannot  result  in  pulling  either  of  the  die  members  out  of  place. 
The  die  opening  is  arranged  with  a  bell-mouth  tapered  from  5 
to  7^  degrees  according  to  the  hardness  of  the  stock  to  be  drawn. 
In  addition  to  making  dies  of  this  type  for  drawing  squares  and 
rectangles,  the  same  type  of  die  may  be  employed  for  drawing 
bars  with  straight  sides  and  semi-circular  sections  at  the  top 

and  bottom.  For  drawing 
hexagons  and  octagons, 
sectional  dies  of  this  type 
are  made  with  the  sections 
adjusted  radially  by 
means  of  screws. 

The  particular  rolling 
mill  die  shown  in  Figs.  9 
and  10  is  for  drawing 
square-shaped  stock,  and 
it  will  be  apparent  that 
four  hardened  steel  rollers 
are  arranged  to  bear 
against  the  four  sides  of 
the  stock  and  reduce  it  to  the  required  diameter.  Obviously 
the  form  of  the  rollers  provides  a  die  opening  corresponding  to 
the  bell-mouth  of  either  a  solid  or  a  "Turk's"  head  die.  The 
opening  in  the  die  can  be  adjusted  to  any  size  within  its  limits 
without  changing  the  rolls,  by  simply  turning  the  square-headed 
screws  provided  for  that  purpose.  These  screws  are  furnished 
with  graduated  dials  to  facilitate  setting. 

Lubricants  Used  on  Drawing  Dies.  —  Lubrication  of  the  steel 
and  cold-drawing  dies  is  very  important.  If  even  a  small  area 
of  steel  is  drawn  into  the  die  without  being  properly  coated  with 
lubricant,  it  will  " seize"  and  do  much  damage  through  scoring 
the  surface  of  the  die  opening.  A  variety  of  different  lubricants 
are  used  on  drawing  dies,  and  each  manufacturer  of  cold-drawn 
screw  stock  and  shafting  has  certain  lubricants  of  which  he  speaks 


Fig.  10.     Opposite  Side  of  Roller  Die 
shown  in  Fig.  9 


COLD-DRAWING  231 

in  high  terms.  At  the  plant  of  the  Pennsylvania  Shafting 
Co.,  two  different  mixtures  are  used  for  lubricating  the  dies. 
One  of  these  is  compounded  from  tallow,  heavy  machine  oil  and 
soap  powder.  These  constituents  are  mixed  in  such  proportions 
that,  when  heated  and  thoroughly  stirred  together,  the  resulting 
lubricant  will  be  of  such  consistency  that  it  can  be  easily  rubbed 
onto  the  bars  by  hand  as  they  are  being  drawn  through  the  die. 
The  other  standard  lubricant  used  by  this  firm  is  made  of  a 
mixture  of  cup  grease,  heavy  machine  oil,  and  soap  powder.  As 
in  the  preceding  case  this  mixture  is  heated  and  thoroughly 
stirred,  and  should  be  of  suitable  consistency  to  be  easily  rubbed 
onto  the  work. 

Liquid  lubricants  are  also  used  in  some  mills.  An  advantage 
resulting  from  their  use  is  that  means  are  devised  for  applying 
the  lubricant  to  the  steel  bars  and  dies  through  which  they  are 
being  drawn  without  requiring  the  workmen  to  apply  grease  by 
hand.  One  way  is  to  take  a  large  bundle  of  waste  and  soak  it 
thoroughly  in  oil,  after  which  the  waste  is  wrapped  around  the 
steel  bar  and  allowed  to  be  drawn  up  against  the  die.  In  this 
way  the  waste  is  held  in  place  against  the  "entering"  side  of  the 
die  and  keeps  the  bar  thoroughly  lubricated  as  it  is  being  drawn 
through.  Care  in  the  application  of  a  lubricant  will  probably 
have  a  greater  effect  upon  the  cost  of  the  lubricant  used  and  the 
efficiency  with  which  it  operates  than  the  selection  of  any  par- 
ticular type  oi  oil  or  grease. 

Straightening  and  Cutting  Cold-drawn  Bars.  —  The  practice 
followed  in  straightening  cold-drawn  bars  naturally  differs  accord- 
ing to  the  diameter  of  the  bar  and  whether  it  was  drawn  in  a 
straight  draw-bench  or  a  bull-block  machine.  In  the  case  of 
shafting  and  bars  drawn  on  the  straight  bench,  the  bars  are 
passed  through  a  straightening  machine,  which  consists  of  a 
rotary  cradle  that  supports  staggered  rolls.  (See  Fig.  1 1 .)  While 
the  shafting  is  being  drawn  through  the  cradle,  the  latter  rotates 
around  the  bar  or  shaft  being  straightened.  The  rollers  impart 
a  fairly  high  polish  to  the  steel  drawn  through  them.  In  the 
case  of  long  coils  of  metal  that  have  been  drawn  on  a  bull-block, 
a  similar  form  of  straightening  machine  is  used,  but,  in  addition, 


232 


IRON   AND    STEEL 


provision  is  made  for  cutting  the  work  into  pieces  of  standard 
length.  For  this  purpose,  the  bar  is  drawn  through  the  rolls 
carried  in  the  rotary  cradle,  and  when  the  end  has  been  drawn 
through  the  required  distance  it  comes  into  contact  with  the 
trip  or  trigger  on  the  machine,  which  results  in  actuating  a 
shear  blade  that  cuts  off  a  piece  of  standard  length.  The 
position  of  this  trigger  may  be  adjusted  to  provide  for  cutting 
off  bars  of  any  required  length,  which  may  be  as  short  as  two 
or  three  inches  or  up  to  practically  any  desired  length. 


Fig.  ii.    Rotary  Type  of  Shaft-straightening  Machine  built  by  Bright- 
man  Mfg.  Co. 

Another  type  of  machine  for  straightening  round  bars,  which 
has  been  found  to  give  very  satisfactory  results,  is  the  Medart 
straightener  built  by  the  Medart  Patent  Pulley  Co.,  St.  Louis, 
Mo.,  shown  in  Fig.  12.  This  machine  has  only  two  rollers,  one 
of  which  is  a  straight  cylinder  and  the  other  slightly  concave. 
These  rollers  are  set  with  their  axes  at  a  slight  angle  to  each 
other  and  the  rollers  are  driven  in  opposite  directions  by  means 
of  universal  joints  and  shafts.  One  end  of  the  bar  to  be  straight- 
ened is  inserted  between  the  rollers,  and  the  angular  position 
of  the  rollers,  combined  with  the  fact  that  they  rotate  in  op- 


COLD-DRAWING 


233 


posite  directions,  results  in  drawing  the  bar  through  the  ma- 
chine at  a  rate  of  from  20  to  30  feet  per  minute.  The  effect  of 
rolling  a  bar  between  the  straight  and  concave  rollers  is  prac- 
tically the  same  as  drawing  the  bar  through  a  set  of  staggered 
rollers  on  the  type  of  straightening  machine  to  which  reference 
has  just  been  made.  The  Medart  straightener  is  adapted  for 
handling  bars  up  to  three  inches  in  diameter,  and  one  feature 
claimed  for  it  is  that  a  particularly  high  polish  is  produced. 

For  straightening  square,  rectangular,  hexagonal,  and  octag- 
onal bars,  a  different  type  of  straightening  machine  must  be  em- 


Fig.  12.     Medart  Straightening  Machine 

ployed  from  those  that  have  been  described.  The  type  of  ma- 
chine used  for  this  purpose  is  shown  in  Fig.  13.  It  consists  of 
two  sets  of  five  pairs  of  staggered  rollers,  those  for  straightening 
the  bars  sidewise  being  located  between  the  housings  of  the  ma- 
chine, while  the  rollers  for  straightening  the  bars  edgewise  are 
located  outside  the  right-hand  housing,  as  shown  in  the  illustra- 
tion. Work  is  passed  through  the  machine  at  a  rate  of  about 
25  feet  per  minute.  The  bars  are  given  two  passes  through 
these  rollers  for  each  pair  of  opposite  sides  of  the  bar,  i.e.,  a 
151 


234 


IRON  AND   STEEL 


square  bar  receives  a  total  of  four  passes,  while  an  octagon- 
shaped  bar  requires  eight  passes  to  completely  straighten  it. 

After  being  straightened  and  polished,  the  steel  is  usually 
wrapped  in  wax  paper  and  then  in  burlap,  so  that  adequate 
protection  is  provided  against  rusting  in  transit.  As  one  of  the 
important  advantages  obtained  by  the  cold-drawing  process  is 
that  the  steel  is  given  a  bright  finish,  it  is  essential  to  protect  it 


Fig.  13. 


Machine  for  Straightening  Square,  Hexagonal, 
Octagonal,  and  Flat  Bars 


against  oxidation.  In  some  cases  the  burlap  bundles  of  stee\ 
are  packecj  in  wooden  boxes  so  that  they  are  held  straight,  thus 
assuring  delivery  to  the  purchaser  in  the  best  possible  condition. 
Cold-rolling  Strip  Steel.  —  Cold-rolled  steel  possesses  several 
advantages  which  cannot  be  secured  with  metal  that  is  rolled 
hot.  Most  noteworthy  of  these  is  the  fact  that  rolling  the 
metal  cold  enables  it  to  be  given  a  so-called  "bright"  finish; 
that  is,  there  is  no  oxide  or  stains  on  its  surface.  Where  the 


COLD-ROLLING  235 

steel  is  rolled  hot,  this  advantage  cannot  be  obtained,  because 
hot  metal  is  easily  attacked  by  oxygen  of  the  air  that  results  in 
forming  the  well-known  scale  with  which  heated  metal  is  cov- 
ered. Those  who  have  had  experience  in  the  working  of  sheet 
steel  know  that  this  oxide  scale  is  exceedingly  hard,  and  that  it 
exerts  a  very  harmful  effect  on  the  dies.  For  this  reason,  cold- 
rolled  steel  is  in  demand  for  use  in  the  manufacture  of  various 
pressed  steel  products.  In  addition  to  the  advantage  secured 
through  the  absence  of  scale  in  working  cold-rolled  steel  under 
the  punch  press,  the  possibility  of  rolling  steel  without  forming 
any  scale  has  another  important  advantage.  Sheet  metal 
produced  in  this  way  can  be  rolled  very  thin  —  the  limit  being 
about  0.003  mcn  —  and  the  thickness  can  be  held  within  close 
limits.  It  will  be  evident  that  this  would  be  utterly  impossible 
if  the  metal  were  at  a  red  heat,  because  the  production  of  scale 
would  not  only  cause  considerable  variation  in  the  gage  of  the 
metal,  but  with  extremely  thin  sheets  it  would  actually  result 
in  its  complete  destruction. 

Mills  engaged  in  the  manufacture  of  cold-rolled  steel  secure 
their  raw  material  in  the  form  of  hot-rolled  ribbon  stock  of  a 
thickness  somewhat  greater  than  that  of  the  cold-rolled  steel 
which  is  to  be  produced.  The  treatment  of  this  material  in 
early  stages  of  the  process  will  differ  according  to  its  carbon  con- 
tent. With  steel  which  does  not  contain  over  0.30  per  cent 
of  carbon,  it  is  unnecessary  to  conduct  a  preliminary  annealing 
process;  but  steel  with  more  than  0.30  per  cent  of  carbon  must 
be  annealed  before  the  rolling  can  be  started.  In  describing  the 
method  of  manufacturing  cold-rolled  steel,  assume  that  the  mill 
is  working  on  high-carbon  steel  which  requires  a  preliminary 
annealing  in  order  to  make  it  soft  enough  to  be  rolled  advanta- 
geously. Three  forms  of  annealing  furnaces  are  employed  for 
this  purpose,  and  the  selection  of  the  particular  form  of  furnace 
to  use  will  depend  upon  the  analysis  of  the  metal.  These 
furnaces  are  known  as  the  "gas  medium"  annealing  furnace, 
the  "pot"  annealing  furnace,  and  the  "muffle"  annealing  fur- 
nace. In  the  muffle  furnace,  the  metal  is  heated  in  contact  with 
the  air,  so  that  an  oxide  scale  is  formed  over  it,  while  in  the  pot 


236  IRON  AND   STEEL 

furnace  and  the  gas  medium  furnace,  the  metal  is  protected  from 
the  air,  so  that  all  tendency  to  oxidize  is  avoided.  One  of  the 
latter  types  of  furnaces  is  generally  used,  but  the  muffle  or 
"scale"  annealing  furnace  is  employed  where  the  stock  which  is 
to  be  converted  into  cold-rolled  steel  has  been  treated  in  such  a 
way  that  its  surface  has  become  decarbonized.  With  such  ma- 
terial, the  production  of  a  scale  on  the  surface  of  the  steel  is  an 
advantage,  because  it  removes  that  part  of  the  metal  from  which 
the  carbon  has  been  withdrawn.  This  will  be  referred  to  in  more 
detail  in  connection  with. the  description  of  the  pickling  process. 
In  all  types  of  furnaces,  the  temperature  employed  varies  from 
1150  to  1300  degrees  F.,  according  to  the  carbon  content  of  the 
steel.  The  methods  to  be  described  are  employed  in  the  produc- 
tion of  cold-rolled  strip  steel  at  the  plant  of  the  Schwartz-Herr- 
mann Steel  Co.,  Floral  Park,  Somerville,  N.  J. 

Annealing  in  a  Gas  Medium  Furnace.  —  The  process  of  an- 
nealing steel  in  the  gas  medium  furnace  consists  primarily  of 
raising  its  temperature  to  the  required  degree  and  then  allowing 
the  metal  to  cool  slowly.  This  result  is  accomplished  by  placing 
the  coils  of  ribbon  stock  on  a  chain  conveyor  which  carries  them 
through  the  furnace.1  The  conveyor  is  driven  by  an  electric 
motor  which  transmits  power  through  a  train  of  high  reduction 
gearing,  so  that  it  takes  about  six  hours  for  the  steel  to  pass 
through  the  furnace.  The  conveyor  carries  the  steel  through 
a  steel  tube  surrounded  with  firebrick  in  the  heating  furnace, 
which  is  built  around  the  portion  of  this  tube  in  which  the 
heating  of  the  steel  is  conducted.  The  furnace  is  of  simple  con- 
struction, consisting  of  a  checkerwork  of  firebrick  which  is  kept 
at  a  red  heat  by  the  combustion  of  producer  gas;  and  in  order 
that  the  furnace  may  operate  at  the  maximum  economy,  the 
draft  in  this  furnace  is  arranged  in  such  a  way  that  the  gas  and 
hot  products  of  combustion  pass  through  the  furnace  in  a  wind- 
ing course  which  has  somewhat  the  form  of  the  letter  S.  In  this 
way,  the  gases  leave  the  furnace  at  a  relatively  low  temperature, 
having  given  up  most  of  their  heat  to  the  brick  checkerwork. 

As  the  essential  difference  between  hot-rolled  and  cold-rolled 
steel  is  that  the  latter  is  entirely  free  from  oxide  scale —  and  as 


COLD-ROLLING 


237 


the  method  of  manufacture  is  carried  on  with  the  view  of  elimi- 
nating scale  —  it  will  be  evident  that  in  the  preliminary  treatment 
of  the  metal  it  is  desirable  to  avoid  scaling  as  far  as  possible. 
Such  being  the  case,  the  annealing  must  be  conducted  in  an 
atmosphere  which  is  free  of  oxygen,  and  this  result  is  obtained 
by  having  the  tube  in  the  annealing  furnace  filled  with  producer 
gas.  This  gas  enters  the  tube  at  one  end  and  passes  through 
to  the  opposite  end,  where  there  is  a  burner  that  provides  for 
consuming  the  gas  as  it  leaves  the  tube.  It  will  be  seen  from 
Fig.  14  that  the  conveyor  tube  rises  at  a  gradual  angle  until  it 


Fig.  14. 


Entering  End  of  Gas  Medium  Furnace  for 
Annealing  Steel 


has  passed  through  the  furnace,  after  which  it  drops  to  the  floor 
level,  where  the  end  of  the  tube  dips  into  a  water  seal  shown  in 
Fig.  15.  In  passing  through  the  portion  of  the  tube  contained 
in  the  furnace,  the  temperature  of  the  steel  is  raised  to  the  degree 
required  by  the  composition  of  the  steel,  after  which  it  is  carried 
along  by  the  slowly  moving  conveyor,  so  that  its  temperature  is 
allowed  to  drop  very  gradually,  and  this  results  in  annealing  the 
steel  so  that  it  is  soft  enough  to  be  worked  under  the  rolls.  The 
steel  is  quite  cold  at  the  time  it  reaches  the  water  seal  at  the  far 
end  of  the  tube,  and  although  it  is  immersed  in  the  water  before 
leaving  the  conveyor,  this  does  not  result  in  the  production  of 
any  serious  amount  of  scale  or  rust.  It  takes  about  six  hours 


238  IRON  AND   STEEL 

for  a  coil  of  steel  to  pass  through  the  furnace,  and  the  rate  of 
production  is  from  15,000  to  20,000  pounds  in  24  hours.  The 
furnace  is  in  operation  continuously. 

Pot  Annealing  Furnace.  —  In  the  pot  annealing  furnace,  as 
in  the  type  of  furnace  which  has  just  been  described,  the  object 
is  to  conduct  the  annealing  operation  in  such  a  way  that  there 
will  not  be  any  tendency  to  form  scale  on  the  metal.  In  pot 
furnaces,  the  coils  of  metal  are  placed  in  steel  pots  and  packed 
with  fine  iron  borings,  after  which  the  cover  is  put  on  the  pot  and 
the  joint  sealed  with  fireclay.  The  iron  borings  serve  to  exclude 


Fig.  15.     Delivery  End  of  Gas  Medium  Furnace — Note 
Arrangement  of  Water  Seal 

air  from  the  pot  and  also  to  assist  in  taking  up  oxygen  from  the 
small  amount  of  air  which  is  left;  in  addition,  they  have  been 
found  to  possess  the  power  of  absorbing  foreign  matter  from  the 
surface  of  the  steel  which  would  otherwise  result  in  the  produc- 
tion of  stains  on  the  bright  surface  of  the  cold-rolled  metal. 
Each  of  the  pots  in  which  the  steel  is  annealed  has  a  capacity 
of  1000  pounds  of  steel  coils,  and  they  are  of  the  form  shown  in 
Fig.  1 6.  There  is  a  draft  up  through  the  center  of  the  pot  and 
lid,  to  allow  the  heat  to  reach  the  metal  from  all  sides.  Eight 
pots  can  be  held  in  each  furnace  at  a  time.  It  takes  about  12 
hours  to  anneal  the  steel  in  this  furnace. 


COLD-ROLLING  239 

The  furnaces  in  which  the  pot  annealing  operation  is  con- 
ducted (see  Fig.  16)  are  similar  in  form  to  muffle  furnaces  except 
that  they  are  provided  with  doors  at  the  front  and  back.  Gas 
and  air  enter  the  furnace  through  ports  arranged  alternately  all 
the  way  down  one  side.  The  flame  rises  to  the  arch  from  which 
it  is  deflected  to  the  opposite  side  of  the  furnace  and  escapes 
through  a  similar  series  of  ports  to  those  through  which  the  air 
and  gas  are  admitted.  When  one  pot  has  been  in  the  furnace 
for  the  required  length  of  time,  the  back  door  is  opened  and  this 
pot  is  withdrawn  and  allowed  to  stand  for  about  18  hours  in 
order  to  allow  the  steel  to  become  quite  cool  before  the  cover  is 


Fig.  1 6.     Pot  Annealing  Furnace,  showing  Pot  just  drawn  out 

taken  off.  After  withdrawing  this  pot,  the  back  door  is  closed 
and  the  front  door  of  the  furnace  is  then  opened  and  a  truck 
carrying  a  pot  of  unannealed  steel  coils  is  pushed  in,  with  the 
result  that  all  the  pots  in  the  furnace  are  moved  toward  the 
back.  It  will  be  evident  from  this  that  the  operation  is  contin- 
uous. Small  "peep  holes"  in  the  furnace  doors  provide  means 
of  viewing  the  interior  of  the  furnace  without  opening  the  large 
door. 

Muffle  Annealing  Furnace.  —  The  muffle  furnace,  in  which 
the  steel  is  given  what  the  cold-rolled  steel-maker  designates  a 
"scale  anneal,"  is  of  exactly  the  same  form  as  the  furnace  in 


240  IRON  AND   STEEL 

which  the  pot  annealing  operation  is  conducted;  but  in  operating 
this  furnace  the  coils  of  steel  are  placed  on  trucks  where  they  are 
exposed  to  the  action  of  an  oxidizing  atmosphere.  These  trucks 
are  passed  through  the  furnace  in  the  same  way  that  trucks 
carrying  the  annealing  pots  are  handled,  and  the  steel  comes  out 
coated  with  an  oxide  scale  which  results  in  removing  a  certain 
amount  of  metal  from  the  surface  of  the  stock  during  the  sub- 
sequent process  of  pickling.  As  previously  mentioned,  this 
method  of  annealing  is  only  employed  in  the  case  of  steel  which 
has  become  decarbonized  at  the  surface,  the  scale  anneal  serv- 
ing to  remove  the  decarbonized  metal.  It  requires  about 
2 \  hours  to  perform  the  annealing  process  in  this  type  of  furnace; 
and  after  being  removed,  three  hours  are  required  for  the  steel 
to  cool  sufficiently  to  be  sent  to 'the  pickling  department.  The 
rate  of  production  is  about  the  same  as  that  of  the  pot  annealing 
furnace. 

Pickling  Stock  before  Cold  Rolling.  —  The  preceding  descrip- 
tion of  the  preliminary  annealing  process  to  which  the  steel  is 
subjected  refers  to  metal  containing  not  less  than  0.30  per  cent 
of  carbon,  and  after  such  steel  has  been  annealed,  it  goes  to  the 
pickling  department,  where  it  is  subjected  to  a  treatment  which 
removes  all  the  oxide  scale  that  was  produced  on  the  metal  during 
the  hot-rolling  operations  by  which  it  was  drawn  out  from  the 
ingot  into  the  form  of  ribbon  stock.  Steel  with  less  than  0.30 
per  cent  of  carbon  does  not  need  a  preliminary  annealing,  but 
goes  direct  to  the  pickling  department.  From  this  it  will  be 
evident  that,  after  annealing,  high-carbon  steel  is  treated  in  the 
same  way  as  steel  with  a  low-carbon  content,  so  that  the  follow- 
ing description  applies  to  both  classes  of  material. 

The  pickling  process  consists  of  immersing  the  rolls  of  steel 
in  vats  of  sulphuric  acid  which  acts  upon  the  metal  and  causes 
the  scale  to  be  removed.  This  acid  is  contained  in  wooden  vats 
which  are  furnished  with  steam  pipes  for  heating  the  acid  so 
that  it  will  act  more  rapidly.  The  acid  consists  of  a  5-per-cent 
solution  of  sulphuric  acid  which  has  a  density  of  66  degrees 
Baume  at  a  temperature  of  60  degrees  F.  In  pickling,  the  coils 
of  steel  must  be  loosened  sufficiently  so  that  the  acid  can  easily 


COLD-ROLLING  241 

find  its  way  between  the  surfaces  of  the  metal.  The  coils  are 
supported  on  wooden  frames  which  are  lifted  by  an  electric  hoist 
that  runs  on  a  track  passing  over  the  vats.  These  frames  are 
dropped  so  that  their  ends  are  supported  by  the  sides  of  the  vat 
while  the  metal  is  immersed.  In  the  case  of  low-carbon  steel, 
the  time  that  the  metal  is  left  in  the  vat  is  not  important,  as  it 
may  be  immersed  for  as  long  as  15  minutes  without  being  dam- 
aged. With  high-carbon  steel,  however,  great  care  must  be 
taken,  as  it  requires  about  three  or  four  minutes  to  remove  the 
scale,  while  leaving  the  steel  in  the  acid  for  a  greater  length  of 
time  will  result  in  withdrawing  carbon  from  the  metal.  The 
removal  of  the  scale  from  the  steel  is  the  result  of  a  combined 
chemical  and  mechanical  action.  The  sulphuric  acid  reacts 
with  the  iron  to  liberate  hydrogen  gas  which  sets  up  a  pressure 
between  the*  steel  and  the  scale  and  results  in  stripping  off  the 
scale.  It  is  important  for  the  stock  to  be  uniformly  covered  with 
scale  before  pickling;  otherwise,  the  pickled  stock  will  have 
a  " pitted"  surface  and,  therefore,  cannot  be  converted  into 
good  cold-rolled  steel. 

After  the  pickling  operation  has  been  completed,  the  steel 
must  be  washed  immediately  in  order  to  remove  the  acid.  This 
is  done  by  lifting  out  the  wooden  frames  from  the  acid  vats  and 
running  them  along  on  the  hoist  so  that  they  may  be  dropped  into 
similar  vats  filled  with  pure  water  which  washes  away  the  acid 
so  that  further  action  upon  the  steel  is  prevented.  The  removal 
of  the  acid  would  probably  be  effectually  done  by  washing  in 
water,  but,  to  make  sure,  the  steel  is  removed  from  the  water 
and  plunged  into  a  vat  containing  a  dilute  solution  of  limewater. 
The  lime  has  the  power  to  neutralize  acid,  but  in  the  case  of 
preparing  steel  for  cold  rolling,  the  use  of  limewater  has  a  fur- 
ther advantage.  This  is  due  to  the  fact  that,  when  the  steel  is 
removed  from  the  vats  and  given  time  to  dry,  it  is  coated  with 
a  film  of  lime  which  keeps  both  air  and  moisture  from  coming 
into  contact  with  the  metal,  and  thus  prevents  it  from  rusting. 

Cold-rolling  Operation.  —  The  cold  rolling  is  done  in  mills  of 
the  type  shown  in  Figs.  17  and  18.  Two  sizes  of  mills  are  used 
which  have  rolls  six  and  eight  inches  in  diameter;  and  although 


242  IRON  AND   STEEL 

both  mills  can  be  used  for  many  sizes  of  stock,  it  is  found  eco- 
nomical to  distribute  the  work  among  the  mills  according  to  its 
size.  In  cold  rolling  it  is  highly  important  to  avoid  chatter  and 
vibration,  as  such  a  condition  would  be  shown  by  irregularities 
in  the  surface  of  the  product.  This  provision  is  well  taken  care 
of  by  having  the  power  transmitted  to  the  rolls  through  herring- 
bone gears  and  shackle  bars  which  serve  as  a  double  precaution 
against  vibration  and  result  in  a  very  uniform  transmission. 
The  rolls  are  made  of  hardened  chrome- vanadium  steel  contain- 
ing a  small  percentage  of  tungsten,  and  are  carefully  ground  to 
give  them  a  very  smooth  finish.  While  in  operation,  the  rolls 


Fig.  17.     Cold-rolling  Strip  Stock 

are  water  cooled  by  a  continuous  stream  of  water  that  flows 
through  a  pocket  in  the  center  of  each  roll.  The  position  of  the 
lower  roll  is  fixed,  while  the  upper  roll  may  be  adjusted  to  pro- 
vide for  the  production  of  metal  of  various  thicknesses.  The 
chief  roller  becomes  very  proficient  in  setting  the  machines  for 
rolling  any  gage  of  metal  and  is  able  to  obtain  very  quickly  the 
required  adjustment.  The  setting  is  made  by  adjusting  the 
rolls  and  testing  the  thickness  of  steel  passed  between  them  with 
a  micrometer;  then,  if  necessary,  further  adjustment  is  made 
until  the  desired  result  is  obtained. 

On  the  entering  side  of  the  mill  there  is  a  frame  which  supports 
an  emery  cloth  wiper  through  which  the  steel  runs  in  order  to 


COLD-ROLLING 


243 


remove  all  foreign  matter  which  might  result  in  damaging  the 
rolls.  The  mills  are  set  to  run  in  opposite  directions,  and  ar- 
ranged in  series  so  that  successive  passes  of  the  metal  may  be 
made  through  adjacent  machines  until  the  desired  reduction  has 
been  obtained.  The  rolls  are  lubricated  with  a  special  grade  of 
oil  known  as  "roll  oil,"  which  is  of  about  the  same  consistency 
as  cylinder  oil,  but  very  carefully  compounded  to  be  sure  that  it 
is  neither  acid  nor  alkaline,  as  either  condition  would  spoil  the 


Fig.  18.     Rolling  Strip  Steel  —  First  Pass  is  made  through  Mill  in 
Background,  and  Second  Pass,  through  Front  Mill 

"bright"  finish  of  the  cold-rolled  steel.  After  each  two  passes 
through  the  mill,  the  steel  must  be  sent  back  to  the  annealing 
furnaces  in  order  to  remove  strains  which  have  been  introduced 
through  the  mechanical  working.  What  is  known  as  "soft" 
steel  is  subjected  to  a  final  annealing  operation  after  it  has  been 
rolled  to  the  required  thickness.  The  "half  hard"  stock  re- 
ceives one  final  pass  through  the  rolls  after  being  annealed.  The 


244  IRON  AND  STEEL 

"hard"  stock  receives  two  passes  through  the  rolling  mill  after 
the  last  annealing  operation  has  been  performed. 

Reduction  of  Stock  by  Rolling.  —  The  amount  of  reduction 
which  can  be  obtained  for  each  pass  through  the  rolling  mills  de- 
pends upon  the  analysis  of  the  steel;  with  low-carbon  steel  the 
reduction  may  be  as  great  as  0.022  inch  for  each  pass,  and  this 
will  be  gradually  decreased  until  the  final  pass  will  only  reduce 
the  thickness  of  the  metal  about  0.005  mcn<-  In  the  case  of 
high-carbon  stock,  the  reduction  at  each  pass  through  the  mill  is 
much  less;  during  the  preliminary  passes,  this  will  amount  to 
not  more  than  o.oio  inch  for  each  pass,  while  the  reduction  will 
be  gradually  decreased  until  the  final  pass  reduces  the  thickness 
of  the  metal  by  only  0.003  mcn-  The  degree  of  accuracy  ob- 
tained in  the  gage  of.  the  metal  is  very  great;  in  the  thicker  gages 
the  variation  will  not  exceed  0.0015  inch,  while  in  the  thinnest 
gages  the  limit  of  error  is  reduced  to  0.00025  inch. 

Trimming  the  Edges  and  Slitting  Stock.  —  After  the  rolling 
operation  has  been  completed,  the  subsequent  treatment  of  the 
cold-rolled  steel  will  depend  upon  the  use  for  which  it  is  intended. 
For  some  purposes  it  is  merely  necessary  to  trim  the  edges  so 
that  the  stock  is  of  uniform  width,  while  in  -other  instances  these 
edges  must  be  finished  in  such  a  way  that  they  are  made  quite 
smooth.  Then,  for  some  uses,  the  steel  must  be  hardened  and 
tempered,  while  other  purchasers  require  it  to  be  "dead  soft." 
Some  customers  of  the  cold-rolled  steel-maker  specify  steel  with 
a  high  polish,  and  others  are  not  particular  about  this  point. 
As  all  of  these  features  are  important  in  cold-rolled  steel  manu- 
facture, they  will  be  described  in  the  order  in  which  the  suc- 
cessive operations  are  performed. 

For  trimming  the  edges  of  the  steel  to  reduce  it  to  uniform 
width,  use  is  made  of  a  rolling  mill  fitted  with  rotary  shear 
blades  which  are  set  at  the  required  distance  apart.  The  steel 
is  passed  through  these  blades  from  a  reel  on  which  the  coil  is 
supported;  and  after  being  reduced  to  standard  width,  it  is 
rolled  up  on  another  reel  at  the  opposite  side  of  the  mill.  At 
the  same  time,  a  second  reel  winds  up  the  trimming  from  the 
edges  of  the  stock,  and  this  scrap  is  pressed  into  bales  and  re- 


COLD-ROLLING  245 

turned  to  the  mill  where  the  hot-rolled  steel  stock  was  produced. 
The  same  form  of  rotary  shear  is  employed  for  slitting  steel  when 
it  is  desired  to  reduce  stock  of  one  width  into  two  or  more  strips 
of  lesser  widths.  The  arrangement  will  be  readily  understood 
by  referring  to  Fig.  19,  which  shows  a  mill  set  up  for  trimming 
the  edges  of  the  stock  and  slitting  it  into  two  narrow  strips. 

Finishing  Edges  of  Stock.  —  When  the  edges  of  the  strip 
steel  must  have  a  smooth  finish,  use  is  made  of  a  simple  but  in- 
genious multiple  filing  machine  which  provides  for  producing  a 


Fig.  19.     Splitting  Wide  Strip  into  Two  Narrow  Strips  and  Trimming 
Edges  —  Note  how  Scrap  is  wound  up  on  Upper  Reel 

smooth  edge  which  may  be  either  square  or  round.  This  machine 
consists  of  a  table  which  supports  a  series  of  cross-slides  made 
of  wood  that  are  grooved  at  both  sides  to  receive  tongues  se- 
cured to  the  table.  The  ends  of  these  slides  are  provided  with 
short  pieces  of  flat  files,  and  the  slides  at  opposite  sides  of  the 
table  are  fitted  with  springs  which  tend  to  draw  them  together. 
In  operation,  the  coil  of  strip  steel,  supported  by  a  reel  at  one  end 
of  the  table,  is  drawn  between  this  series  of  files  and  is  then  wound 
on  a  reel  at  the  opposite  end.  It  will  be  evident  that,  in  passing 
between  the  files,  the  edges  of  the  steel  are  smoothed  down; 


246  IRON  AND   STEEL 

and  by  having  all  the  files  perpendicular  to  the  plane  of  the  steel 
a  square  edge  is  imparted,  while  arranging  the  files  at  a  variety 
of  different  angles  results  in  rounding  the  edges  of  the  stock. 

Cutting  Strips  into  Stock  Lengths.  —  After  the  edges  of  the 
cold-rolled  steel  have  been  trimmed  —  and  finished  in  cases 
where  this  operation  is  necessary  —  some  of  the  strip  steel  is  cut 
up  into  standard  stock  lengths.  For  this  purpose  a  measuring 
bench  and  shear  are  used.  The  coil  of  steel  is  mounted  on  a  reel 
and  the  steel  is  pulled  between  the  shear  blades  so  that  a  piece  of 
the  required  length  may  be  cut  off,  the  length  being  indicated 
by  a  scale  marked  on  the  bench  for  that  purpose.  With  this 
machine,  one  man  and  a  helper  can  very  rapidly  cut  up  steel 
into  any  lengths  which  may  be  required. 

Hardening  and  Tempering.  —  Purchasers  of  cold-rolled  steel 
who  use  the  material  for  making  springs,  and  for  various  other 
purposes,  specify  steel  which  has  been  tempered;  and  for  this 
purpose  the  cold-rolled  steel-maker  must  provide  his  mill  with 
equipment  for  doing  this  work.  One  successful  method  of  heat- 
treatment  is  applied  as  follows:  The  steel  in  the  form  of  a  coil 
is  mounted  on  a  reel  and  connected  with  a  " leader"  which 
provides  for  drawing  it  through  the  heating  and  quenching 
mediums  at  the  proper  speed.  The  steel  is  first  run  through  a 
lead  bath  and  its  temperature  raised  to  about  1450  degrees  F., 
according  to  the  analysis  of  the  steel,  after  which  it  is  quenched 
in  oil;  then  the  steel  passes  on  through  a  second  lead  bath  which 
provides  for  drawing  the  temperature  at  from  780  to  800  degrees 
F.,  after  which  the  metal  is  wound  on  a  second  reel.  A  vari- 
able-speed motor  is  used  for  drawing  the  steel  through  the  fur- 
nace, and  this  motor  transmits  power  through  a  series  of  herring- 
bone reduction  gears  which  provide  for  drawing  the  steel  through 
at  exactly  the  proper  speed. 

When  the  steel  has  been  tempered,  it  passes  onto  the  reels 
shown  in  Fig.  20,  upon  which  the  coils  of  steel  are  wound.  It 
will  be  evident  from  this  illustration  that  provision  is  made  for 
heat-treating  eight  coils  of  steel  simultaneously.  All  the  reels 
shown  are  driven  from  a  single  motor,  power  being  transmitted 
through  a  train  of  high-reduction  herringbone  gears  which  pro- 


COLD-ROLLING  247 

vide  for  drawing  the  steel  through  the  hardening  and  tempering 
baths  at  the  proper  speed. 

The  preceding  description  applies  to  the  method  of  heating 
the  thicker  gages  of  steel;  in  the  case  of  the  thinner  gages, 
exactly  the  same  method  and  form  of  equipment  are  employed, 
except  that  the  metal  is  quenched  in  a  lead  bath  which  is  kept 
just  above  the  melting  point,  i.e.,  at  about  630  degrees  F. 
This  results  in  making  the  steel  practically  " glass  hard."  The 
object  of  quenching  the  thin  steel  in  a  lead  bath  is  that  it  avoids 


Fig.  20.     Reels  on  which  Strip  Steel  is  wound  after  Heat- 
treating  Operation  is  completed 

the  tendency  to  crack  and  become  very  crooked,  which  is  a 
constant  source  of  trouble  where  the  steel  is  hardened  in  oil. 

Polishing  Cold-rolled  Steel.  —  For  certain  purposes,  there  is 
a  demand  for  cold-rolled  steel  with  a  high  polish,  and  to  meet 
the  requirements  of  such  users,  the  steel  is  taken  from  the  hard- 
ening and  tempering  department  and  subjected  to  a  polishing 
treatment.  This  is  done  on  machines  provided  with  a  series  of 
rolls  over  which  the  steel  runs,  one  of  these  machines  being 
shown  in  Fig.  21.  Upon  entering,  it  passes  through  a  box 


248  IRON  AND   STEEL 

containing  moist  emery  powder  which  must  be  extremely  fine, 
powder  from  No.  80  to  No.  100  being  generally  used.  The 
steel  carries  away  some  of  this  emery  with  it,  and  in  passing  over 
the  basswood  rolls,  a  rubbing  action  takes  place  which  imparts 
a  high  polish  to  the  steel.  Upon  leaving  the  machine,  the  metal 
passes  between  a  series  of  wipers  which  effectually  remove  any 
emery  which  is  left  on  the  metal. 

Cold-rolled  strip  steel  is  made  by  the  Schwartz-Herrmann 


Fig.  21.     Special  Polishing  Machine  designed  for  Applying  High 
Finish  to  Strip  Steel 


Steel  Co.  in  widths  ranging  from  f  up  to  4^  inches;  and  the 
thickness  of  the  product  covers  a  range  from  0.003  to  0.083  inch. 
On  the  thicker  gages,  the  steel  is  guaranteed  to  come  within 
0.0015  inch  of  the  specified  thickness;  and  this  limit  of  error  is 
gradually  reduced,  so  that  it  is  possible  to  furnish  the  thinnest 
stock  with  a  guarantee  that  the  error  in  thickness  does  not 
amount  to  more  than  0.00025  inch.  To  any  experienced  me- 
chanic, it  will  at  once  be  apparent  that  the  possibility  of  securing 
such  a  high  degree  of  accuracy  can  only  result  through  exercising 


WIRE  DRAWING  249 

absolute  care  in  carrying  out  every  step  of  the  process  of  manufac- 
ture. 

Wire  Drawing.  —  After  wire  rods  have  been  rolled  down  to 
the  smallest  practicable  size,  smaller  diameters  are  produced  by 
means  of  drawing  the  wire  rod  through  a  plate  or  die  provided 
with  a  hole  which  reduces  the  size  to  the  desired  diameter. 
Wire  drawing  has  been  practiced  for  centuries  along  lines  very 
similar  to  those  still  employed.  It  is  definitely  known  that 
there  was  a  wire  drawing  mill  in  Nuremberg,  Germany,  in 
1370.  The  first  wire  drawing  mill  in  America  was  built  in  1775 
in  Norwich,  Conn. 

Iron  and  Steel  wire  is  generally  drawn  from  No.  5  rod,  which  is 
0.207  inch  in  diameter.  The  rods  are  wound  on  reels,  as  men- 
tioned in  the  preceding  paragraphs,  into  coils  weighing  from 
150  to  300  pounds.  The  rods,  as  delivered  by  the  rolling  mill, 
are  covered  with  scale,  and  the  first  process,  therefore,  is  'to 
place  the  wire  rod  coils  for  a  short  time  in  a  pickling  bath  of 
dilute  sulphuric  acid,  heated  to  a  boiling  heat  by  steam  coils. 
This  solution  loosens  the  scale  which  is  then  washed  off  with  a 
stream  of  water.  The  bundles  are  next  dipped  in  a  limewater 
solution  and  are  then  placed  in  a  "dry  house"  or  " baker, " 
where  they  are  subjected  to  a  temperature  of  from  300  to  400 
degrees  F.  for  several  hours.  A  thin  coat  of  the  limewater 
solution  adheres  to  the  rods  and  lubricates  the  wire  as  it  passes 
through  the  dies.  If  the  wire  rod  is  not  thoroughly  freed  of  the 
scale,  or  is  not  thoroughly  covered  with  lime,  the  die  hole  will 
be  quickly  worn  larger  than  the  correct  size,  and  the  wire  will 
be  scratched,  out  of  round,  or  of  increasing  gage.  If  the  wire 
rod  is  left  in  the  sulphuric-acid  solution  too  long,  it  becomes 
brittle  and  the  surface  is  hardened.  The  wire  rod  also  becomes 
brittle  if  removed  from  the  dry  house  too  soon.  Brittleness  may 
be  removed,  however,  by  leaving  the  rods  in  the  dry  house  longer 
than  would  otherwise  be  necessary. 

Wire-drawing  Machines.  —  Briefly  described,  the  machines 
used  for  wire  drawing  consist  of  a  die  or  drawplate  provided  with 
holes  through  which  the  wire  is  drawn,  and  means  for  pulling 
the  wire  through  these  dies  and  winding  it  upon  a  reel.  The 


250 


IRON  AND   STEEL 


wire-drawing  machines  may  be  either  of  the  single-block  or 
continuous  types.  A  single-block  machine  is  shown  in  Fig.  22. 
It  consists  mainly  of  a  table  T  to  which  is  fastened  a  bracket  B, 
which  holds  the  die  or  drawplate,  and  a  power-driven  vertical 
drum  or  block  D  on  which,  as  it  rotates,  the  wire  is  wound  after 
having  been  pulled  through  the  die.  Before  the  drawing  can 
begin,  the  wire  is  pointed  so  that  the  operator  can  push  the  end 
of  it  through  the  drawplate.  The  pointing  is  done  in  a  special 
pointing  machine.  After  that,  the  wire  is  pushed  through  that 


Machinery 


Fig.  22.     Single-block  Wire-drawing  Machine 

hole  in  the  drawplate  which  is  of  the  correct  diameter  to  which 
the  wire  is  to  be  reduced,  and  then  pulled  through  this  hole,  by 
power,  by  means  of  tongs  F,  a  chain  G,  and  a  clutch  C,  for  a 
distance  of  about  two  or  three  feet.  Then  the  end  of  the  wire  is 
attached  to  the  block  D,  upon  which  the  drawn  wire  will  be 
wound,  and  the  block  is  set  in  motion  by  means  of  bevel  gearing 
A  and  shaft  E.  The  wire  will  thus  be  pulled  through  the  draw- 
plate  and  reduced  to  the  required  diameter.  The  block  is 
slightly  tapered  so  that  the  coil  of  wire  can  be  easily  removed 
from  it  when  completed.  Continuous  wire-drawing  machines 


WIRE  DRAWING  251 

have  a  series  of  dies  through  which  the  wire  passes.  Between 
each  two  dies,  the  wire  is  wound  over  pulleys  or  blocks,  as 
otherwise  it  would  be  impossible  to  pull  the  wire  through  suc- 
cessive dies.  The  speed  at  which  wire  drawing  is  done  varies 
according  to  the  material  and  the  amount  of  reduction.  As  an 
average,  it  varies  from  60  feet  per  minute  for  slow  speeds  in 
single-block  machines  to  900  feet  per  minute  with  the  high 
speeds  possible  in  continuous  machines. 

When  drawing,  the  wire  is  lubricated,  oil,  tallow,  and  soap 
water  being  used  for  this  purpose.  Smaller  sizes,  especially  of 
music  wire,  are  drawn  wet  or  very  thoroughly  lubricated,  the 
reels  of  wire,  in  this  case,  being  set  into  tubs  containing  the  lu- 
bricating solution  of  soap  water,  and  drawn  directly  from  the 
submerged  reels  through  the  drawplate.  The  wire  is  reduced  in 
diameter  for  each  drawing  or  pass  by  one  number  on  the  stand- 
ard wire  gage  scale.  When  the  wire  is  drawn  through  the  holes 
in  the  dies,  thus  reducing  its  diameter,  its  surface  becomes  hard 
and  brittle,  and  the  wire  is,  therefore,  annealed  at  frequent  in- 
tervals before  it  is  reduced  to  a  smaller  size  by  a  subsequent 
drawing  operation. 

Drawplates.  —  The  drawplate  or  die  for  larger  sizes  of  wire  is 
generally  made  from  chilled  cast  iron  or  tool  steel,  or  from  a 
high-grade  tungsten  steel  into  which  a  number  of  holes  of  dif- 
ferent sizes  are  drilled  and  reamed.  The  holes  taper,  having  the 
correct  diameter  of  the  wire  to  be  drawn  at  that  face  of  the  draw- 
plate  which  is  towards  the  block  or  pulley.  For  smaller  sizes  of 
wire,  the  dies  are  made  from  less  expensive  or  imperfect  varieties 
of  diamonds,  and  are  known  as  " diamond  dies."  Generally 
speaking,  wire  drawn  to  not  less  than  0.040  inch  in  diameter  is 
drawn  through  chilled  cast-iron  or  tungsten  steel  drawplates, 
while  wire  of  from  0.040  down  to  0.002  inch  in  diameter,  which 
is  the  smallest  commercial  size  ordinarily  drawn,  is  produced  by 
diamond  dies  inserted  in  a  brass  body.  The  large  sizes  of  wire 
are  more  often  drawn  on  single-block  machines,  while  the  smaller 
sizes  are  drawn  on  continuous  machines.  The  size  of  diamond 
for  wire  0.040  inch  in  diameter  is  about  3  or  3!  carats,  while  J- 
carat  stones  will  suffice  for  dies  for  drawing  wire  o.oio  inch  in 


252  IRON  AND    STEEL 

diameter.  The  life  of  the  diamond  die  used  for  drawing  steel 
wire  averages  only  about  three  days.  The  life  depends  solely 
upon  the  length  of  wire  passed  through  it;  the  speed  at  which 
the  wire  is  drawn  appears  to  have  little  effect  on  it.  About 
200  pounds  of  steel  wire  can  be  drawn  through  a  No.  32  Brown 
&  Sharpe  gage  diamond  die  before  its  size  is  too  large  for  further 
use;  but  only  15' pounds  of  wire  can  be  drawn  through  holes  of 
from  6.003  to  0.005  mcn  m  diameter,  and  less  than  one  pound  can 
be  drawn  through  holes  smaller  than  0.002  inch.  When  the 
diamond  dies  are  worn  too  much,  they  are  re-drilled  for  a  larger 
gage  number.  In  drilling  the  diamonds,  the  average  time  for 
enlarging  a  hole  o.ooi  inch  in  diameter  is  about  ij  hour.  For 
hard  music  wire,  diamonds  of  comparatively  large  size  are  re- 
quired; thus  for  holes  as  small  as  0.005  incn  m  diameter,  2-  to 
2j-carat  diamonds  are  used. 

Annealing  the  Wire.  —  Wire  is  drawn  cold,  that  is,  the  metal 
is  at  ordinary  temperatures;  this  gives  a  bright  finish  and 
renders  polishing  unnecessary.  The  repeated  drawings  through 
the  dies  increase  the  ultimate  strength,  but  lessen  the  ductility 
in  almost  the  same  ratio.  In  this  condition,  the  wire  is  known 
as  "hard-drawn."  Because  of  this  loss  of  ductility,  metal  that 
is  to  be  drawn  through  several  dies  before  it  becomes  of  the  de- 
sired size  must  be  annealed.  The  annealing  may  be  done  by 
placing  the  bundles  of  wire  in  a  muffle  furnace,  or  in  large  iron 
or  steel  cylindrical  pots  which  are  hermetically  sealed  and 
heated  by  coal  fires.  Care  must  be  taken  that  the  wire  is 
thoroughly  and  uniformly  annealed.  In  the  case  of  steel  wire, 
it  is  also  necessary  to  see  that  the  steel  is  not  burnt  or  over- 
heated. While  annealing  restores  the  ductility  of  the  wire,  it 
reduces  the  ultimate  strength.  It  is  generally  necessary  to 
anneal  wire  after  it  has  been  drawn  through  three  or  four  dies. 

In  the  so-called  " patent  process,"  the  wire  is  passed  through 
a  long  furnace  in  which  it  is  heated  to  approximately  1800 
degrees  F.  As  it  emerges  from  this,  it  is  cooled  by  the  air. 
Sometimes  the  wire  issuing  from  this  furnace  is  passed  through 
a  lead  bath  that  is  maintained  at  a  temperature  of  from  800  to 
900  degrees  F.  The  wire  in  either  case  has  the  best  working 


WIRE  DRAWING  253 

combination  of  tensile  strength  and  toughness  obtainable  and 
may  be  given  greater  "drafts,"  or  reductions,  in  the  die  than 
wire  annealed  in  the  ordinary  manner. 

Wire  Gages.  —  The  size  of  wire  is  generally  indicated  by 
gage  numbers.  There  is  a  great  multiplicity  of  different  wire 
gages  in  use.  Upon  the  recommendation  of  the  Bureau  of  Stand- 
ards at  Washington,  a  number  of  the  principal  wire  manufacturers 
and  consumers  have,  however,  agreed  to  designate  the  American 
Steel  &  Wire  Co.'s  gage,  which  is  the  same  as  the  Washburn  & 
Moen  and  the  Roebling  gage,  as  the  "Steel  Wire  Gage"  or  the 
"U.  S.  Steel  Wire  Gage";  hence,  this  gage  may  be  considered 
standard  for  steel  wire  in  the  United  States.  For  copper  wire 
and  wires  of  other  metals,  the  "American  Wire  Gage,"  which 
is  also  known  as  the  " Brown  &  Sharpe  Gage,"  is  standard. 
For  music  or  piano  wire,  the  gage  known  as  "American  Steel  & 
Wire  Co.'s  Music  Wire  Gage"  is  adopted  as  standard  in  the 
United  States  upon  the  recommendation  of  the  United  States 
Bureau  of  Standards.  The  standard  wire  gage  in  Great  Britain 
is  that  known  as  "British  Standard  Wire  Gage,"  also  known  as 
"New  British  Standard,"  the  "English  Legal  Standard,"  and 
the  "Imperial  Wire  Gage." 

The  Birmingham  or  Stubs  iron  wire  gage  is  now  nearly  ob- 
solete and  is  little  used,  either  in  Great  Britain  or  the  United 
States.  Stubs  steel  wire  gage,  used  for  drill  rod,  however,  is 
still  extensively  used.  Tables  of  these  various  wire  gages  wiH 
be  found  in  all  standard  engineering  handbooks. 


CHAPTER  XI 
STRUCTURAL   CARBON  AND   ALLOY   STEELS 

STEEL  may  be  divided  into  two  large  general  classes,  according 
to  the  use  to  which  it  is  put;  these  are  known  as  tool  steel  and 
structural  steel.  The  former  class,  in  its  widest  sense,  includes 
all  those  steels  that  are  used  for  cutting  tools,  while  the  latter 
class  includes  those  steels  that  are  mainly  used  in  the  making  of 
machinery  and  the  building  of  structures.  Applied  in  this 
sense,  structural  steel  includes  both  carbon  steels  and  alloy 
steels  used  in  machine  construction,  bridges,  etc. 

Structural  Carbon  Steel.  —  The  carbon  steel  used  for  struc- 
tural purposes  contains  a  smaller  amount  of  carbon  than  that 
used  for  tool  steel,  and  is  generally  referred  to  as  " low-carbon" 
or  " medium- carbon"  steel.  It  is  generally  made  either  by  the 
Bessemer  or  the  open-hearth  process.  The  term  "structural 
steel"  is  also  used  in  a  narrower  sense,  referring  only  to  the  steel 
used  for  the  construction  of  buildings,  bridges,  etc.  The  prop- 
erties and  requirements  of  steel  of  this  kind  are  dealt  with  in  the 
closing  paragraphs  of  Chapters  VII  and  VIII,  on  Bessemer 
steel  and  open-hearth  steel,  respectively.  The  carbon  steel 
dealt  with  in  this  chapter  will  be  that  mainly  used  in  machine 
construction,  which  may  also  be  made  either  by  the  Bessemer  or 
the  open-hearth  processes,  and  which  may  or  may  not  be  heat- 
treated  to  increase  the  strength  or  toughness,  or  casehardened 
to  increase  the  resistance  to  wear,  after  it  has  been  machined 
to  the  proper  shape  required  for  the  machine  for  which  it  is 
intended. 

Carbon  steels  for  structural  purposes  are  made  with  carbon 
contents  varying  all  the  way  from  o.io  to  i.oo  per  cent.  That 
containing  o.io  per  cent  of  carbon  is  usually  known  by  the  trade 
name  "soft  basic  open-hearth  steel."  The  o.2o-per-cent  car- 

254 


STRUCTURAL  STEELS  255 

bon  steel  is  generally  known  as  " machine  steel."  Steels  con- 
taining 0.30,  0.40,  and  0.50  per  cent  of  carbon  are  also  made  for 
structural  purposes.  Steel  with  a  higher  carbon  content  than 
this  is  seldom  used  as  a  structural  steel,  except  steel  containing 
from  0.80  to  i.oo  per  cent  of  carbon,  which  is  known  as  " spring 
steel,"  and  is  generally  used  for  springs.  The  heat-treatment 
to  which  the  carbon  steels  containing  from  0.20  to  0.25  per  cent 
of  carbon  are  generally  subjected,  when  these  steels  are  em- 
ployed for  parts  exposed  to  wear,  is  known  as  "casehardening. " 
Casehardening.  —  Casehardening  is  a  process  for  hardening 
the  surface  of  low-carbon  steel.  High-carbon  steel  will  harden 
by  being  heated  to  a  certain  temperature  and  suddenly  quenched 
in  water,  brine,  or  oil.  Low-carbon  steel  will  not  harden  ap- 
preciably if  treated  in  this  manner,  and  the  process  of  case- 
hardening,  therefore,  consists  in  first  increasing  the  carbon  con- 
tent of  the  surface  of  the  low-carbon  steel  so  that  it  can  be 
hardened  by  being  quenched.  The  surface,  or  case,  only  will  be 
high  enough  in  carbon  to  be  hardened,  and  the  interior,  or  the 
core,  will  still  be  low  in  carbon  and  soft.  Small  machine  parts 
are  generally  casehardened  in  quantity,  the  process  being  briefly 
as  follows:  The  parts  are  packed  in  cast-iron  or  welded  sheet- 
steel  boxes,  together  with  some  material  containing  carbon  such 
as  charcoal,  charred  leather,  powdered  bone,  etc.  The  low- 
carbon  steel  will  absorb  carbon  on  its  surface  from  this  material, 
when  the  box  and  its  contents  are  heated  to  a  temperature  of 
from  1600  to  1800  degrees  F.  for  a  certain  length  of  time,  de- 
pending upon  the  depth  of  hardened  surface  desired  and  the 
nature  of  the  material.  The  absorption  of  carbon  begins  when 
the  steel  reaches  about  1300  degrees  F.,  but  commercially  car- 
burizing  must  be  done  at  a  higher  temperature.  The  length  of 
time  at  which  the  steel  should  be  held  at  the  carbur-izing  tem- 
perature after  the  required  degree  of  heat  has  been  reached 
may  vary  from  two  to  six  hours.  At  the  end  of  the  carburizing 
period,  the  box  is  withdrawn  from  the  furnace  and  allowed  to 
cool  slowly.  The  articles  are  then  taken  out  of  the  carburizing 
mixture,  placed  in  a  muffle  furnace,  and  reheated  to  about  1500 
degrees  F.,  after  which  they  are  quenched  in  water  or  oil.  For 


256  IRON  AND   STEEL 

ordinary  purposes,  clear  cold  water  is  satisfactory.  Salt  water 
or  brine  is  used  when  a  very  hard  surface  is  desired,  and  the  oil 
bath  when  a  hard  surface  is  not  as  important  as  a  tough  core. 

The  method  of  casehardening  just  described  is  probably  the 
most  common  method,  but  when  a  hard  case  is  the  only  re- 
quirement, the  articles  may  be  quenched  directly  after  car- 
burizing  by  emptying  the  contents  of  the  casehardening  boxes 
directly  into  cold  water  or  oil,  but  in  this  way  both  the  core  and 
the  case  are  coarsely  crystallized  and  the  strength  is  reduced. 
Allowing  the  box  and  its  contents  to  cool  and  then  reheating, 
prior  to  quenching,  givts  more  satisfactory  results  than  when 
the  parts  are  dumped  directly  into  the  quenching  bath  at  the 
end  of  the  carburizing  period. 

When  it  is  desired  to  increase  the  toughness  and  the  strength 
of  the  casehardened  article  and  refine  the  case  as  well,  it  should 
be  subjected  to  a  double  reheating  after  carburizing;  that  is, 
it  should  first  be  carburized  and  permitted  to  cool  slowly  in  the 
carburizing  mixture,  then  reheated  to  about  1500  degrees  F. 
and  quenched  in  water  or  oil,  and  again  reheated  to  about 
1400  degrees  F.  and  quenched  in  water  or  oil.  Finally,  the 
temper  is  drawn  in  oil  at  any  temperature  varying  from  300  to 
450  degrees  F.  according  to  the  hardness  desired. 

Instead  of  packing  the  material  to  be  casehardened  in  a  car- 
bonaceous mixture,  casehardening  is  now  also  done  by  placing 
the  articles  to  be  carburized  in  a  revolving  drum  or  retort  through 
which  a  current  of  carbonaceous  gas  is  forced.  The  retort  serves 
as  a  muffle  and  is  surrounded  by  the  flames  of  the  heating  gases. 
It  is  claimed  that  by  gas  carburizing,  small  pieces  can  be  car- 
burized much  more  quickly  and  at  about  one-half  the  cost  as 
compared  with  packing  in  iron  boxes  and  heating.  Carbon 
monoxide  has  been  found  to  be  a  suitable  gas  for  gas  carburizing, 
except  that  it  has  an  oxidizing  effect  that  might  spoil  small  parts 
which  cannot  be  ground  afterwards.  Another  process  has, 
therefore,  been  developed,  in  which  the  work  is  packed  with 
wood  charcoal  in  a  cylinder  and,  when  Cheated  to  the  carbur- 
izing temperature,  a  current  of  carbon  dioxide  is  injected  into 
the  cylinder. 


STRUCTURAL   STEELS  257 

Steels  for  Casehardening.  —  The  percentage  of  carbon  in 
steels  ordinarily  used  for  parts  to  be  casehardened  varies,  as  a 
general  rule,  from  0.15  to  0.25  per  cent.  For  general  work,  steel 
of  the  following  composition  will  be  found  satisfactory:  Car- 
bon from  0.15  to  0.20  per  cent;  manganese,  less  than  0.35  per 
cent;  silicon,  less  than  0.30  per  cent.  The  sulphur  and  phos- 
phorus should  be  as  low  as  possible.  If  the  carbon  exceeds 
0.20  per  cent,  it  tends  to  give  a  hard  instead  of  a  soft  core. 
On  the  other  hand,  if  the  carbon  content  is  too  low,  the  steel  may 
be  difficult  to  machine;  hence,  steels  containing  as  much  as 
from  0.20  to  0.25  per  cent  of  carbon  are  generally  used. 

Degree  and  Depth  of  Hardened  Surface.  —  The  percentage 
of  carbon  contained  in  the  casehardened  surface  varies  accord- 
ing to  the  requirements.  For  most  purposes,  0.90  per  cent  of 
carbon  is  preferable.  A  case  containing  i.io  per  cent  of  carbon 
gives  a  very  hard  wearing  surface  that  is  suitable  for  work 
that  must  withstand  a  fairly  constant  pressure,  as  shafts  running 
in  bearings,  etc.;  but  this  amount  of  carbon  will  render  parts 
that  must  withstand  repeated  shocks  too  brittle;  for  this  work, 
the  case  should  not  contain  more  than  from  0.90  to  i.oo  per  cent 
carbon. 

The  percentage  of  carbon  in  the  hardened  crust  varies  with 
the  depth  of  the  latter;  therefore,  the  deeper  the  penetration, 
the  higher  must  be  the  carbon  content  near  the  surface.  Crusts 
about  0.050  inch  deep  usually  have  from  0.85  to  0.90  per  cent  of 
carbon  on  the  surface.  In  many  instances,  a  penetration  of 
0.04  inch  is  sufficient,  but  if  the  work  is  to  be  ground  after  case- 
hardening  it  should  be  carburized  to  a  depth  of  about  0.060 
inch.  Too  deep  a  carburized  case  makes  the  work  more  brittle, 
partly  because  of  the  prolonged  exposure  to  a  high  temperature 
and  partly  because  of  the  increase  in  the  hardened  section  and 
the  decrease  in  the  softer  and  more  ductile  core;  hence,  parts 
to  withstand  bending  stresses,  like  gear  teeth,  should  not  be 
carburized  too  deeply.  Carburization  takes  place  rapidly  until 
the  crust  is  saturated  with  carbon  (about  0.90  per  cent  of  carbon 
marks  the  saturation  point),  when  there  is  a  sudden  diminution 
in  the  rate  of  carburization,  which  varies  according  to  the  tem- 


258  IRON  AND   STEEL 

perature.  The  penetration  of  the  carbon  increases  with  the 
temperature  and  with  the  time  of  exposure,  but  not  in  direct 
proportion  to  these  two  factors. 

Casehardening  for  Colors.  —  When  desired,  such  parts  as 
wrenches,  etc.,  may  be  hardened  and  colored  at  the  same  time. 
The  parts  to  be  colored,  however,  must  be  well  polished  and 
must  not  be  handled  with  greasy  hands.  For  this  purpose, 
the  following  mixture  may  be  used:  10  parts  of  charred  bone, 
6  parts  of  wood  charcoal,  4  parts  of  charred  leather,  and  i  part 
of  powdered  cyanide.  The  leather  should  be  black,  crisp,  and 
well  pulverized,  and  the  four  ingredients  well  mixed.  The 
object  in  charring  the  bone  and  leather  is  to  remove  all  grease. 
If  the  colors  obtained  are  too  gaudy,  the  cyanide  may  be  omitted, 
and  if  there  is  still  too  much  color,  the  charcoal  may  be  left  out. 
Another  mixture  consists  of  10  parts  of  granulated  bone,  2  parts 
of  boneblack,  and  i  part  of  granulated  charred  leather.  The 
parts  to  be  colored  and  hardened  may  be  packed  in  a  piece  of 
gas  pipe  having  a  closed  end.  Pipe  is  preferable,  because  the 
pieces  can  be  dumped  into  the  cooling  water  with  little  or  no 
exposure  to  the  air.  The  work  should  then  be  heated  to  a 
dark  cherry-red  for  about  four  or  five  hours;  if  the  temperature 
is  too  high,  no  colors  will  appear.  A  compressed-air  pipe  should 
be  connected  with  the  water  pipe  to  the  cooling  tank  in  such  a 
way  that  a  jet  of  air  is  forced  upward,  thus  filling  the  tank  with 
bubbles.  There  should  also  be  a  sieve  or  basket  in  the  tank  for 
receiving  the  work.  After  quenching,  the  parts  should  be  placed 
in  boiling  water  for  five  minutes  and  then  buried  in  dry  sawdust 
for  half  an  hour. 

Cleaning  Work  after  Casehardening.  —  Work  having  crev- 
ices in  which  dirt  is  likely  to  stick  after  Casehardening  may  be 
cleaned  by  washing  in  a  solution  of  i  part  of  caustic  soda  to 
10  parts  of  water.  In  making  this  solution,  the  soda  should 
be  put  into  hot  water  gradually,  and  the  mixture  stirred  until 
the  soda  is  thoroughly  dissolved.  A  more  effective  method  is 
to  place  the  work  into  a  mixture  of  i  part  of  sulphuric  acid 
to  2  parts  of  water  for  about  three  minutes,  and  then  wash 
immediately  in  a  soda  solution. 


STRUCTURAL  STEELS  259 

Properties  and  Uses  of  Structural  Carbon  Steel.  —  When  in 
the  following  paragraphs  the  elastic  limit  per  square  inch  and 
other  properties  of  different  kinds  of  steels  are  given,  these  refer 
to  bars  about  one  square  inch  in  sectional  area;  where  two 
figures  are  given  for  elastic  limit  or  other  properties,  the  high 
elastic  limits  can  be  obtained  only  on  sections  of  this  size,  or 
smaller,  with  very  careful  heat-treatment,  while  the  low  elastic 
limits  may  be  expected  on  heavier  sections. 

Carbon  Steel  with  o.io  per  cent  Carbon.  —  Steel  with  o.io 
per  cent  of  carbon  is  commonly  used  for  seamless  tubing,  pressed 
steel  parts,  etc.  It  is  known  in  the  trade  as  "soft  basic  open- 
hearth  steel,"  and  is  particularly  useful  for  the  purposes  men- 
tioned, because  it  is  soft  and  ductile,  and  can  be  drawn  and 
shaped,  to  a  great  extent,  without  cracking.  It  should  contain 
about  0.45  per  cent  of  manganese;  the  contents  of  neither  phos- 
phorus nor  sulphur  should  exceed  0.04  per  cent.  In  its  annealed 
condition,  this  steel  has  an  elastic  limit  of  from  30,000  to  35,000 
pounds  per  square  inch,  with  a  reduction  in  area  of  from  55  to 
65  per  cent,  and  an  elongation  in  two  inches  of  from  30  to  40 
per  cent.  It  should  not  be  used  where  a  great  deal  of  strength  is 
required;  but  the  quality  of  the  material  may  be  improved  by 
cold-drawing;  in  its  natural  or  annealed  condition,  it  cannot  be 
easily  machined,  as  it  is  likely  to  tear  when  turned,  threaded, 
or  broached.  Heat-treatment  does  not  increase  its  strength,  but 
does  slightly  increase  its  toughness.  The  only  heat-treatment 
of  any  value  is  to  heat  the  steel  to  about  1500  degrees  F.  and 
quench  it  in  oil  or  water.  It  need  not  be  drawn  afterwards. 
It  is  not  suitable  for  casehardening,  although  it  may  be  case- 
hardened  to  some  extent,  if  required.  If  cold-drawn,  and  after- 
wards heated,  it  will  return  to  the  characteristics  of  the  an- 
nealed material,  the  same  as  all  materials  the  elastic  limit  of 
which  have  been  increased  by  cold-working. 

Carbon  Steel  with  0.20  per  cent  Carbon.  —  Steel  with  0.20 
per  cent  of  carbon  is  generally  known  in  the  trade  as  "machine 
steel,"  and  is  used  mainly  for  such  machine  parts  as  require 
casehardening  after  machining,  as  the  steel  is  especially  adapted 
for  this  process.  This  steel  should  contain  about  0.65  per  cent 


260  IRON  AND   STEEL 

of  manganese,  and  the  phosphorus  and  sulphur  content  should 
not  exceed  0.04  per  cent.  It  can  be  used  the  same  as  the  o.io- 
per-cent  carbon  steel  for  cold  pressed  shapes,  and  can  be  drawn 
into  tubes  and  rolled  into  cold-rolled  forms.  It  is  especially 
used  for  forged  and  machined  casehardened  parts,  as  it  forges 
and  machines  well,  but  it  is  not  used  when  great  strength  is  re- 
quired. When  in  its  annealed  condition,  it  has  an  elastic  limit 
of  from  30,000  to  40,000  pounds  per  square  inch,  a  reduction  in 
area  of  from  45  to  60  per  cent,  and  an  elongation  in  2  inches  of 
from  25  to  35  per  cent.  When  heat-treated,  the  elastic  limit 
can  be  increased  to  from  40,000  to  75,000  pounds  per  square 
inch,  but  the  reduction  in  area  is  changed  to  from  15  to  50  per 
cent,  and  the  elongation  in  two  inches  to  from  15  to  30  per  cent. 

This  steel  may  be  casehardened  in  two  ways.  Parts  which  are 
not  subjected  to  heavy  load  or  shocks,  but  simply  must  have  a 
hard  surface,  may  be  heat-treated  as  follows:  Carburize  at  a 
temperature  of  from  1600  to  1700  degrees  F.  and  cool  slowly,  or 
quench  in  oil.  Then  reheat  to  from  1450  to  1500  degrees  F.  and 
quench  in  oil.  Parts  which  must  not  only  be  hard  on  the  sur- 
face, but  which  should  also  have  considerable  strength,  as,  for 
example,  gears,  should  have  a  double  heat- treatment  as  follows: 
Carburize  at  a  temperature  of  from  1600  to  1700  degrees  F.  and 
cool  slowly  in  the  carburizing  packing  material.  Then  reheat 
to  from  1500  to  1550  degrees  F.  and  quench  in  oil,  and  reheat  for 
a  second  time  to  from  1400  to  1450  degrees  F.,  and  quench  in  oil. 
Finally,  draw  in  hot  oil  to  a  temperature  of  from  300  to  450 
degrees  F.,  according  to  the  degree  of  hardness  required.  The 
heat-treatment  does  not  increase  the  ultimate  strength  in  any 
appreciable  degree,  but,  because  of  the  refinement  of  the  grain, 
it  increases  the  elastic  limit. 

Carbon  Steel  for  Screw  Machine  Work.  —  Steel  suitable  for 
screw  machine  work  is  generally  known  as  " screw  stock,"  and 
contains  generally  from  0.18  to  0.25  per  cent  of  carbon.  It 
should  contain  from  0.30  to  0.80  per  cent  of  manganese;  not 
over  o.i 2  per  cent  of  phosphorus;  and  from  0.06  to  0.12  per  cent 
of  sulphur.  Machine  parts  requiring  great  strength  and  tough- 
ness cannot  be  made  from  this  material,  and  most  small  parts 


STRUCTURAL   STEELS  261 

made  from  it,  such  as  screws,  etc.,  should  be  heat-treated,  the 
heat-treatment  consisting  of  heating  to  1500  degrees  F.  and 
quenching  in  oil  or  water;  then  reheating  to  from  600  to  1300 
degrees  F.  and  permitting  the  steel  parts  to  cool  down  slowly. 
The  material  may  also  be  casehardened  in  about  the  same  way 
that  the  regular  o.2o-per-cent  carbon  steel  is  casehardened. 
Screw  stock  is  made  either  in  the  form  of  cold-rolled  or  hot- 
rolled  bars.  Cold-rolled  bars  are  much  stronger  and  may  some- 
times be  used  without  heat- treatment;  but  hot-rolled  screw 
stock  should  always  be  heat-treated. 

Carbon  Steel  with  0.30  per  cent  Carbon.  —  Steel  containing 
0.30  per  cent  of  carbon  is  used  in  machine  construction  for  axles, 
shafts,  and  other  structural  parts  which  require  strength  as 
well  as  toughness.  This  steel  is  heat-treated  to  increase  its 
elastic  limit,  but  is  not  generally  used  for  casehardening  pur- 
poses, although  it  may  be  casehardened,  if  required.  It  can 
easily  be  forged  and  machined.  This  steel  should  have  the  same 
composition  with  regard  to  manganese,  phosphorus,  and  sul- 
phur as  the  o.2o-per-cent  carbon  steel.  In  its  annealed  state, 
it  has  a  strength  of  from  35,000  to  45,000  pounds  per  square 
inch,  a  reduction  in  area  of  from  40  to  55  per  cent,  and  an  elon- 
gation in  two  inches  of  from  20  to  30  per  cent.  In  its  heat- 
treated  condition,  it  has  an  elastic  limit  of  from  40,000  to  80,000 
pounds  per  square  inch,  with  a  reduction  in  area  and  elongation 
practically  the  same  as  in  the  annealed  condition. 

This  steel  may  be  subjected  to  either  a  single  or  double  re- 
heating. The  heat-treatment  in  the  first  case  consists  of  heating 
to  about  1500  degrees  F.  and  quenching  in  oil  or  water,  and  re- 
heating to  from  600  to  1200  degrees  F.,  and  permitting  the  metal 
to  slowly  cool.  The  double  reheating  heat-treatment  consists 
of  heating  the  steel  to  from  1500  to  1550  degrees  F.,  quenching 
in  oil  or  water;  reheating  to  from  1400  to  1450  degrees  F.,  and 
again  quenching;  after  which  the  steel  is  again  reheated  to 
from  600  to  1 200  degrees  F.  and  slowly  cooled.  When  used  for 
casehardening,  the  steel  should  be  heat-treated  in  the  same 
way  as  in  the  double  reheating  process,  but,  in  addition,  should 
be  drawn  in  oil  to  a  temperature  of  from  300  to  450  degrees  F. 


262  IRON  AND   STEEL 

Carbon  Steel  with  0.40  per  cent  Carbon,  —  Steel  containing 
0.40  per  cent  of  carbon  is  used  for  such  machine  parts  as  require 
a  high  degree  of  strength  and  toughness.  In  automobiles,  for 
example,  it  is  used  for  crankshafts  and  driving  shafts.  It  has 
also  been  used  for  automobile  transmission  gears,  but  is  not 
quite  suitable  for  this  purpose,  because  it  is  not  hard  enough  with- 
out casehardening,  and,  when  casehardened,  does  not  possess 
enough  toughness.  The  manganese,  phosphorus,  and  sulphur 
content  should  be  about  the  same  as  that  in  the  o.2o-per-cent 
carbon.  In  its  annealed  condition,  its  elastic  limit  varies  from 
40,000  to  50,000  pounds  per  square  inch;  the  reduction  in  area, 
from  40  to  50  per  cent;  and  the  elongation  in  two  inches,  from 
20  to  25  per  cent.  When  heat-treated,  the  elastic  limit  varies 
from  45,000  to  100,000  pounds  per  square  inch;  the  reduction 
in  area,  from  25  to  50  per  cent;  and  the  elongation  in  two  inches, 
from  5  to  25  per  cent.  When  annealed,  this  steel  can  be  easily 
machined,  but  is  not  suitable  for  automatic  screw  machine  work. 
When  heat-treated,  it  should  be  subjected  to  a  double  reheating. 
It  should  first  be  heated  to  from  1500  to  1550  degrees  F.  and 
slowly  cooled.  It  is  then  reheated  to  from  1400  to  1450  degrees 
F.  and  quenched  in  oil  or  water,  and  finally  reheated  to  from  600 
to  1 200  degrees  F.  and  slowly  cooled. 

Carbon  Steel  with  0.50  per  cent  Carbon.  —  Except  for  the 
increased  carbon  content,  this  steel  has  the  same  composition 
as  the  o.2o-per-cent  carbon  steel.  In  its  annealed  condition, 
it  has  an  elastic  limit  varying  from  45,000  to  60,000  pounds  per 
square  inch;  a  reduction  in  area,  from  30  to  40  per  cent;  and 
an  elongation  in  two  inches,  of  from  15  to  20  per  cent.  When 
heat-treated,  its  elastic  limit  is  raised  to  from  50,000  to  110,000 
pounds  per  square  inch,  but  the  reduction  in  area  and  the  elong- 
ation are  generally  decreased.  It  should  be  subjected  to  the 
same  heat-treatment  as  the  o.4o-per-cent  carbon  steel.  It  is 
somewhat  more  difficult  to  machine  than  the  steels  with  a  lower 
carbon  content,  but  is  generally  used  for  the  same  purposes  as 
the  o.4o-per-cent  carbon  steel. 

Spring  Steel. — The  steel  generally  known  as  " spring  steel" 
contains  from  0.80  to  i.oo  per  cent  of  carbon.  These  steels  are 


STRUCTURAL  STEELS  263 

always  used  in  a  heat-treated  condition,  and  have,  when  heat- 
treated,  an  elastic  limit  of  from  90,000  to  160,000  pounds  per 
square  inch.  The  o.8o-per-cent  carbon  steel  is  generally  used 
for  springs  of  light  section.  Its  composition,  in  addition  to  the 
carbon,  should  be  about  0.35  per  cent  of  manganese  and  not 
more  than  0.04  per  cent  of  either  phosphorus  or  sulphur.  The 
heat-treatment  of  the  spring  after  shaping  or  coiling  consists 
in  heating  to  from  1425  to  1475  degrees  F.,  and  quenching  in 
oil,  after  which  the  spring  is  reheated  to  from  400  to  800  degrees 
F.,  according  to  the  degree  of  temper  desired.  Steel  contain- 
ing from  0.95  to  i.oo  per  cent  of  carbon  is  used  considerably  for 
the  heavier  types  of  springs.  It  is  heat-treated  in  a  manner 
similar  to  that  used  in  the  o.8o-per-cent  carbon  steel,  but  the 
first  heating,  previous  to  quenching  in  oil,  should  be  at  a  tem- 
perature slightly  less  than  that  used  for  the  o.8o-per-cent  carbon 
steel. 

The  Pennsylvania  Railroad  specifications  for  spring  steel  re- 
quire a  carbon  content  not  under  0.90  per  cent;  manganese, 
from  0.25  to  0.50  per  cent;  silicon,  not  over  o.io  per  cent;  phos- 
phorus, 0.05  per  cent,  but  not  over  0.07  per  cent;  and  sulphur, 
not  over  0.03  per  cent. 

The  United  States  Navy  Department  specifies  that  spring 
steel  must  be  made  either  by  the  open-hearth,  crucible,  or  elec- 
tric process.  The  carbon  content  must  vary  between  0.70  and 
i.io  per  cent;  the  manganese,  between  0.25  and  0.50  per  cent; 
the  silicon  content  must  not  exceed  0.25  per  cent;  and  that  of 
sulphur  and  phosphorus  must  not  exceed  0.04  per  cent.  The 
ultimate  tensile  strength,  after  heat-treatment,  must  be  at  least 
180,000  pounds  per  square  inch  and  the  elastic  limit  must  be 
at  least  75  per  cent  of  the  ultimate  tensile  strength.  The 
following  tests  are  prescribed:  A  heat-treated  bar,  resting  on 
supports  24  inches  between  centers,  must  not  take  a  perma- 
nent set  of  more  than  0.050  inch  after  the  first  application  of  a 
load  which  will  produce  a  fiber  stress  of  135,000  pounds  per  square 
inch.  When  a  load  which  will  produce  a  fiber  stress  of  160,000 
pounds  per  square  inch  is  applied,  the  permanent  set  must  not 
be  more  than  7.5  per  cent  of  the  total  deflection,  and  after  five 


264  IRON  AND   STEEL 

additional  applications  of  a  load  producing  a  fiber  stress  of  150,000 
pounds  per  square  inch,  there  must  be  no  further  set.  With 
regard  to  the  variation  in  size  of  bars  of  spring  steel,  the  Navy 
Department  has  issued  the  following  regulations:  In  round 
bars,  a  variation  of  0.020  inch  in  diameter  is  allowable;  in  rec- 
tangular bars,  a  variation  of  0.020  inch  in  thickness  and  0.030 
inch  in  width,  from  the  sizes  ordered,  will  be  permitted.  These 
specifications  do  not  apply  to  drawn,  round,  or  square  wire  below 
TV  inch  in  diameter  or  size,  nor  to  flat  bars  below  f\  inch  thick. 

Structural  Alloy  Steels.  —  The  term  "  alloy  steel  "  is  applied 
to  steels  which  contain  some  metallic  element  other  than  iron, 
which  gives  to  them  peculiar  or  characteristic  properties.  The 
metals  added  to  steel  to  form  alloy  steels  are  chromium,  cobalt, 
manganese,  molybdenum,  nickel,  titanium,  tungsten,  vanadium, 
and  uranium.  Of  these  the  alloys  with  chromium,  manganese, 
nickel,  titanium,  and  vanadium  are  structural  steels,  while  the 
alloys  with  cobalt,  molybdenum,  tungsten,  and  uranium  are 
used  for  cutting  tools;  that  is,  they  are  tool  steels  of  the  ''high- 
speed steel"  class.  Some  of  the  latter  steels  also  contain  chro- 
mium and  vanadium.  In  addition  to  the  alloy  steels  composed 
mainly  of  one  metallic  element  outside  of  iron,  there  are  alloy 
steels  consisting  of  two  or  even  three  metallic  elements  besides 
iron.  The  most  common  of  the  structural  steels  thus  composed 
are  chrome-nickel  or  nickel  chromium  steel,  and  chrome-vana- 
dium steel.  Only  the  structural  steels  will  be  dealt  with  in  this 
chapter,  the  high-speed  steels  being  treated  in  Chapter  XII. 

Alloy  steels  have  become  extensively  used  during  the  last 
decade  and  are  likely  to  displace  structural  carbon  steels  for  im- 
portant structural  purposes,  where  a  decrease  in  weight  for 
equal  strength  is  of  importance,  as  in  the  construction  of  auto- 
mobiles, bridges,  ships,  etc.  It  is,  however,  only  possible  to 
obtain  the  increased  strength  in  alloy  steels  by  proper  heat- 
treatment.  In  their  annealed  state  they  are  not  much  superior 
to  ordinary  carbon  steel.  The  heat-treatment  of  alloy  steels, 
therefore,  is  one  of  the  most  important  branches  of  the  indus- 
tries making  use  of  this  material.  Alloy  steels  may  be  made  by 
the  open-hearth,  crucible,  or  electric  process. 


STRUCTURAL  STEELS  265 

Chromium  Steel.  —  Alloy  steels  containing  only  chromium 
as  the  alloying  metal  are  not  used  to  any  great  extent  for 
structural  purposes,  as  chromium  is  generally  not  used  alone, 
but  in  combination  either  with  nickel  or  with  vanadium.  There 
are  few  purposes,  however,  for  which  a  chromium  steel  is  used 
without  other  metallic  additions,  as,  for  example,  for  armor- 
piercing  projectiles,  for  which  it  is  extensively  used.  It  is  also 
employed  in  rock-crushing  machinery  and  in  the  construction 
of  safes,  where  alternate  layers  of  soft  wrought  iron  and  chro- 
mium steel  are  employed.  Chromium  is  usually  present  in 
chromium  alloy  steels  In  amounts  from  2  to  5  per  cent,  the  per- 
centage of  carbon  varying  from  0.8  to  2  per  cent.  The  properties 
brought  out  by  heat-treatment  in  this  steel  are  an  intense  hard- 
ness combined  with  a  very  high  elastic  limit,  so  that  the  metal 
is  peculiarly  adapted  to  withstand  violent  shocks. 

Manganese  Steel.  —  Manganese  steel,  also  known  as  Had- 
field's  steel  on  account  of  having  first  been  produced  by  the 
Hadfield  firm  in  England,  is  composed  of  from  n  to  14  per  cent 
of  manganese;  from  i.o  to  1.3  per  cent  of  carbon;  from  0.3  to 
0.8  per  cent  of  silicon;  and  from  0.05  to  0.08  per  cent  of  phosphor- 
us. The  sulphur  content  should  be  so  low  as  to  be  negligible, 
as  it  is  eliminated  in  making  the  steel  by  the  manganese  forming 
a  sulphide  which  rises  to  the  surface  and  enters  the  slag.  There 
are  manganese  steels  having  different  compositions  from  that 
mentioned  above,  but  the  steel  having  the  composition  given 
is  that  commercially  known  as  " manganese  steel."  If  there 
should  be  only  about  1.5  per  cent  of  manganese,  the  steel  will 
be  very  brittle  and  this  brittleness  increases  until  the  manganese 
content  reaches  about  5  per  cent,  when  the  brittleness  is  so 
extreme  that  the  steel  can  be  pulverized  under  a  hammer. 
Greater  percentages  of  manganese,  however,  make  the  steel 
ductile  and  hard  and  a  manganese  content  of  about  12  per  cent 
brings  out  these  qualities  to  the  best  advantage.  Manganese 
steel  is  melted  and  cast  in  molds.  After  having  been  cast,  it  is 
subjected  to  a  heat-treatment  consisting  of  heating  the  steel 
to  about  1900  degrees  F.  and  then  cooling  it  as  quickly  as  possible 
by  immersing  in  cold  water.  The  more  sudden  the  cooling  the 


266  IRON  AND   STEEL 

better.  The  average  commercial  manganese  steel  when  heat- 
treated  has  a  tensile  strength  of  from  80,000  to  90,000  pounds 
per  square  inch,  an  elastic  limit  of  from  45,000  to  60,000  pounds 
per  square  inch,  and  an  elongation  of  about  30  per  cent.  The 
Hadfield  firm  in  England,  however,  has  produced  rolled  man- 
ganese steel  having  a  tensile  strength  of  150,000  pounds  per 
square  inch,  an  elongation  of  50  per  cent,  and  a  reduction  of  area 
of  nearly  40  per  cent.  The  elastic  limit  of  this  steel,  however, 
was  only  about  56,000  pounds  per  square  inch.  Manganese 
steel  has  the  peculiar  property  of  being  practically  non-magnetic 
and  hence  is  used  for  purposes  which  require  a  hard  non-magnetic 
metal. 

The  rolling  and  forging  of  manganese  steel  proved  a  difficult 
operation  for  many  years,  and  it  was  not  used  except  in  its  cast 
form.  At  present,  however,  large  ingots  are  rolled  into  rails 
and  other  shapes.  The  heat-treatment  of  the  rolled  steel  is 
similar  to  that  of  the  cast  material.  It  is  extremely  difficult  to 
machine  and,  as  a  rule,  is  finished  by  grinding.  It  is  used  mostly 
for  castings  subjected  to  heavy  strains  and  especially  to  excessive 
wear,  such  as  the  wearing  parts  of  steam  shovels,  rock  crushers, 
ore  crushers,  and  other  mining  machinery.  It  is  also  used 
in  the  making  of  safes,  and  to  a  limited  extent  for  rails,  frogs, 
and  crossings,  but  the  steel  is  expensive  and  only  where  it  cuts 
down  a  high  maintenance  cost  is  its  use  economical.  It  is 
stated  that,  for  screening  coke  when  woven  screens  of  manganese 
steel  bars  are  used,  their  life  is  a  hundred  times  as  great  as  that 
of  screens  made  of  the  soft  carbon  steel  generally  used. 

Manganese  steel  has  a  very  low  conductivity  for  both  heat 
and  electricity,  a  low  melting  point  (about  2480  degrees  F.)  and 
a  very  high  coefficient  of  expansion.  When  cast,  it  is  brittle, 
and,  after  heat- treatment,  its  tensile  strength  is  only  moderate, 
with  a  low  elastic  limit  in  both  tension  and  compression  and  a 
rather  high  ductility;  its  shearing  strength  is  remarkably  high. 
When  rolled  or  forged  and  heat-treated,  the  tensile  strength  of 
manganese  steel  is  increased  greatly,  and  the  ductility  is  much 
improved.  The  rolled  material,  if  not  heat-treated,  is  quite 
brittle. 


STRUCTURAL  STEELS  267 

The  ductility  of  the  metal  is  increased  by  quenching,  which  is 
entirely  opposite  to  the  result  that  would  be  obtained  with  car- 
bon steels.  While  manganese  steel  is  so  hard  that  no  steel  tool 
can  cut  it,  castings  and  forgings  made  of  it  may  be  bent  and 
hammered  like  mild  steel.  The  chief  characteristic  of  manganese 
steel  is  its  extreme  hardness,  because  of  which  it  cannot  be  ma- 
chined. Owing  to  the  low  elastic  limit,  the  metal  can  be  made 
to  pean,  or  flow,  when  cold,  by  hammering.  The  tendency  of  the 
steel  to  flow  under  heavy  loads  prevents  its  being  used  for  rail- 
way car  wheels.  It  is,  however,  widely  used  under  light  loads  in 
mine  and  quarry  cars,  blast-furnace  charging  buggies,  etc.  In 
a  way,  therefore,  the  steel  is  soft,  and  hardness  tests  that  de- 
pend upon  indenting  the  material  do  not  give  high  figures;  yet 
its  resistance  to  most  kinds  of  wear  is  extraordinarily  great. 

The  simplest  and  cheapest  way  to  produce  manganese  steel 
is  to  blow  in  the  Bessemer  converter  molten  8o-per-cent  ferro- 
manganese  and  molten  soft  steel  containing  from  o.io  to  0.25 
per  cent  of  carbon.  The  carbon  content  of  the  ferromanganese 
brings  up  the  steel  to  the  correct  composition  as  regards  carbon. 
A  manganese  steel  recently  placed  on  the  market  contains  only 
from  6  to  9  per  cent  of  manganese,  yet  it  is  said  to  possess  the 
characteristic  hardness  and  ductility  of  steel  having  a  higher 
manganese  content.  Its  composition  is  based  on  the  theory 
that  a  certain  relation  exists  between  the  percentage  of  the 
manganese  and  the  percentage  of  the  carbon  employed  with  it 
in  the  steel,  and  that  the  proportioning  of  the  carbon  ingredients 
in  accordance  with  this  relation  gives  a  steel  with  the  desired 
characteristics.  This  steel  is  made  in  the  usual  manner;  it  is 
a  poor  conductor  of  heat  and  is  practically  nonmagnetic. 

Nickel  Steel.  —  Nickel  steel  is  one  of  the  most  important  of 
the  structural  alloy  steels.  The  most  common  grades  contain 
from  3  to  5  per  cent  of  nickel  and  from  o.io  to  0.50  per  cent  of 
carbon.  The  steel  most  generally  used  contains  3.5  per  cent  of 
nickel,  but  the  carbon  content  varies  by  0.05  per  cent  all  the  way 
from  0.15  to  0.50  per  cent  of  carbon,  according  to  the  purpose 
for  which  the  steel  is  intended.  Generally  speaking,  when  nickel 
steel  is  properly  heat-treated,  it  combines  great  tensile  strength 


268  IRON  AND   STEEL 

and  hardness  with  a  high  elastic  limit  and  ductility.  For  this 
reason,  it  has  been  used  for  armor  plate,  because  it  does  not  crack 
when  perforated  by  a  projectile.  It  is  largely  used  in  automobile 
construction  and  has  been  employed  in  bridge  construction  and 
for  rails  and  ammunition.  Nickel  steel  rails  resist  abrasion 
better  than  ordinary  Bessemer  or  open-hearth  rails  —  so  much 
so  in  fact  that  it  has  been  claimed  that  one  nickel-steel  rail  will 
outlast  four  Bessemer  rails.  It  is  also  used  for  marine  shafting 
where  its  strength  and  ductility  make  it  valuable  on  account  of 
the  high  and  sudden  stresses  that  are  frequently  imposed  on 
propeller  shafts. 

The  Society  of  Automobile  Engineers  (now  the  Society  of 
Automotive  Engineers)  prescribes  in  a  report  of  January,  1912, 
that  3-50-per-cent  nickel  steel  shall  contain,  in  addition  to  its 
carbon  content,  from  0.50  to  0.80  per  cent  of  manganese,  and 
not  more  than  0.04  per  cent  of  either  phosphorus  or  sulphur. 
The  properties  of  nickel  steel  depend,  in  addition  to  its  nickel 
content,  upon  the  carbon  percentage;  o.i5-per-cent  carbon 
nickel  steel  in  its  annealed  condition  will  have  an  elastic  limit  of 
from  35,000  to  45,000  pounds  per  square  inch  and,  in  its  heat- 
treated  condition,  an  elastic  limit  of  from  40,000  to  80,000 
pounds  per  square  inch.  The  o.3o-per-cent  carbon  nickel  steel 
in  its  annealed  condition  has  an  elastic  limit  of  from  45,000 
to  55,000  pounds  per  square  inch,  and,  when  heat-treated,  an 
elastic  limit  of  from  65,000  to  150,000  pounds  per  square  inch; 
while  the  o.5o-per-cent  carbon  nickel  steel,  annealed,  has  an 
elastic  limit  of  from  55,000  to  70,000  pounds  per  square  inch, 
and,  heat-treated,  an  elastic  limit  of  from  70,000  to  200,000 
pounds  per  square  inch.  The  elongation  in  two  inches  varies 
from  25  to  35  per  cent  in  the  annealed  o.i5-per-cent  carbon 
nickel  steel  to  from  15  to  25  per  cent  in  the  annealed  0.50-per- 
cent steel;  the  elongation  of  the  heat-treated  steel  varies  from 
X5  to  35  per  cent  in  the  o.i5-per-cent  carbon  nickel  steel,  and 
from  5  to  20  per  cent  in  the  o.5o-per-cent  steel. 

All  nickel  steel  may  be  heat-treated  either  by  a  single  or 
double  heat- treatment.  In  the  first  case,  it  is  heated  to  from 
1500  to  1550  degrees  F.  and  quenched  in  oil  and  water,  and  then 


STRUCTURAL  STEELS  269 

reheated  to  from  600  to  1200  degrees  F.  and  slowly  cooled.  In 
the  second  case,  it  is  heated  to  from  1500  to  1550  degrees  F. 
and  quenched,  and  then  reheated  to  from  1300  to  1400  degrees 
F.,  and  again  quenched,  and  finally  reheated  to  from  600  to  1200 
degrees  F.  and  slowly  cooled.  Nickel  steel  containing  from  0.15 
to  0.25  per  cent  of  carbon  may  also  be  casehardened.  The 
casehardening  is  carried  out  as  follows:  Carburize  at  a  tem- 
perature of  from  1650  to  1700  degrees  F.  and  cool  slowly  in  the 
carburizing  mixture;  then  reheat  to  from  1450  to  1525  degrees 
F.  and  quench;  reheat  again  to  from  1300  to  1400  degrees  F. 
and  quench;  and  finally  temper  at  a  temperature  of  from  250 
to  500  degrees  F.,  according  to  the  hardness  of  the  case  required 
on  the  casehardened  material,  and  cool  slowly. 

The  o.i5-per-cent  carbon  nickel  steel,  when  casehardened, 
produces  an  exceedingly  tough  and  strong  core  and  a  hard  sur- 
face. It  is  used  for  casehardened  gears  and  other  casehardened 
parts  which  require  both  strength  and  hardness.  The  steels 
containing  from  0.20  to  0.25  per  cent  of  carbon  are  considered 
the  best  quality  of  nickel  steels.  That  with  0.20  per  cent  of 
carbon  is  a  good  casehardening  steel,  and  that  with  0.25  per 
cent  of  carbon  may  also  be  successfully  casehardened  and  has 
been  found  suitable  for  gears;  it  is  used  to  a  large  extent  for 
automobile  transmissions.  Nickel  steel  containing  0.30  per 
cent  of  carbon  is  used  for  shafts  and  axles  requiring  strength  and 
toughness.  In  automobiles,  for  example,  it  is  used  for  crank- 
shafts, driving  shafts,  and  transmission  shafts.  It  is  not  suitable 
for  casehardening,  although  it  may  be  casehardened.  Nickel 
steel  with  0.35  per  cent  of  carbon  is  used  for  the  same  purposes 
as  the  o.3o-per-cent  carbon  steel.  The  nickel  steels  with  higher 
carbon  content  are  not  used  to  any  large  extent.  By  proper 
heat-treatment  they  may  be  made  harder  than  the  steels  with 
lower  carbon  content,  but  the  brittleness  is  increased. 

Titanium  Steels.  —  Titanium  steel  contains  from  0.5  to  i 
per  cent  of  titanium.  This  steel  is  used  for  gears,  locomotive 
tires,  rails  and  castings,  its  special  property  being  its  ability  to 
resist  abrasion  and  frictional  wear.  Titanium  steel  bars  may 
also  be  made  that  have  exceptional  resistance  to  torsional  strains. 


270  IRON  AND  STEEL 

One  example  is  cited  where  a  bar  4  feet  long  and  ij  inch  square 
was  twisted  through  seven  complete  revolutions  without  sign 
of  fracture.  In  a  structural  steel  having  a  tensile  strength  of 
67,000  pounds  per  square  inch  and  an  elastic  limit  of  42,000 
pounds  per  square  inch,  an  addition  of  0.5  per  cent  of  titanium 
increased  the  tensile  strength  to  77,000  pounds  per  square  inch, 
and  the  elastic  limit  to  51,700  pounds  per  square  inch.  The 
elongation  and  reduction  of  area  was  also  slightly  increased; 
at  least,  there  was  no  decrease  in  these  values.  It  is  stated  that 
titanium  steel  rails  will  wear  only  one-fifth  as  much  as  ordinary 
Bessemer  rails  under  the  same  conditions  in  an  equal  period  of 
time. 

When  titanium  is  used  in  cast  iron,  0.5  per  cent  of  titanium  is 
said  to  increase  the  crushing  strength  of  gray  iron  by  50  per 
cent.  It  has  also  been  added  with  success  in  the  crucible  process 
to  tool  steels,  giving  the  cutting  tools  much  greater  ductility 
and  qualities  somewhat  resembling  those  of  high-speed  steel. 
In  steel  castings  it  is  also  easier  to  obtain  a  high  tensile  strength 
and  elastic  limit  when  introducing  titanium. 

Vanadium  Steel.  —  Vanadium  is  used  in  steel  either  alone  or 
in  combination  with  chromium.  Vanadium  steels  in  which 
vanadium  is  used  alone  usually  contain  from  0.15  to  0.25  per  cent 
of  vanadium.  The  steel  is  valuable  on  account  of  its  shock- 
resisting  ability  and  is  frequently  used  where  exposed  to  repeated 
stresses.  Vanadium  increases  the  tensile  strength  and  the  elastic 
limit,  and  steel  containing  vanadium  is  used  for  springs,  gears 
subjected  to  severe  service,  car  axles,  hammer  piston  rods, 
aeroplane  parts,  etc.  As  a  rule,  however,  vanadium  steel  also 
contains  chromium  which  is  exceptionally  valuable,  as  it  com- 
bines a  high  elastic  limit  with  great  hardness.  Vanadium  is  also 
used  largely  in  tool  steels  both  for  cutting  tools  and  for  dies  for 
forging  machines. 

Chrome-vanadium  Steel.  —  Chrome-vanadium  steel  combines 
the  properties  obtained  by  adding  chromium  and  vanadium 
separately  to  steel.  The  chromium  increases  the  hardness  and 
the  elastic  limit  and  the  vanadium  the  shock-resisting  capacity; 
hence,  the  resulting  steel  is  one  in  which  the  properties  of  hard- 


STRUCTURAL  STEELS  271 

ness  and  strength  are  combined  with  ability  to  resist  shocks  and 
repeated  stresses.  Chrome-vanadium  steel  should  contain  about 
0.90  per  cent  of  chromium  and  0.18  per  cent  of  vanadium;  the 
vanadium  content  should  never  be  less  than  0.12  per  cent. 
Different  properties  are  given  to  this  steel  by  varying  the  amount 
of  carbon.  Commonly  used  steels  have  carbon  contents  vary- 
ing from  0.15  to  0.50  per  cent  of  carbon.  Neither  the  sulphur 
nor  the  phosphorus  content  should  exceed  0.04  per  cent.  The 
manganese  content  should  be  about  0.65  per  cent.  The  chrome- 
vanadium  steels  that  contain  from  0.15  to  0.20  per  cent  of  carbon 
are  used  mainly  for  casehardened  parts.  The  o.25-per-cent  car- 
bon steel  may  be  casehardened,  but  is  not  suitable  for  this  purpose. 
This  steel,  as  well  as  those  having  a  higher  percentage  of  carbon, 
are  used  for  a  number  of  purposes  where  in  the  past  plain  car- 
bon and  nickel  steels  were  used;  they  are  heat-treated,  but  not 
casehardened.  Chrome- vanadium  steel  containing  as  much 
as  0.40  per  cent  of  carbon  is  used  when  a  high  degree  of  strength 
is  required  in  combination  with  a  moderate  degree  of  toughness, 
as,  for  example,  for  high-duty  shafts.  The  0.45-  and  o. 50-per- 
cent carbon  chrome-vanadium  steels  are  suitable  for  gears  and 
springs. 

The  heat-treatment  to  which  chrome-vanadium  steels  are 
subjected  vary  according  to  the  percentage  of  carbon  present. 
The  o.i5-per-cent  carbon  steel,  when  casehardened,  is  treated 
as  follows:  Carburize  at  a  temperature  of  from  1650  to  1700 
degrees  F.  and  cool  slowly  in  the  carburizing  mixture;  then  re- 
heat to  from  1600  to  1700  degrees  F.  and  quench;  and  reheat 
again  to  from  1475  to  X55°  degrees  F.  and  quench.  Then  heat 
for  tempering  to  from  250  to  550  degrees  F.  and  cool  slowly. 

When  heat-treated  for  strength  only,  the  same  steel  should 
be  treated  as  follows:  Heat  to  from  1600  to  1700  degrees  F. 
and  quench  in  oil,  and  then  reheat  to  some  temperature  between 
500  and  1300  degrees  F.  and  cool  slowly.  All  chrome- vanadium 
steels  with  a  carbon  content  of  0.40  per  cent  and  less  are  treated 
in  the  same  manner. 

When  heat-treated  for  strength,  the  0.45-  and  o.5o-per-cent 
carbon  chrome-vanadium  steels  are  held  for  about  one-half  hour 


272  IRON  AND   STEEL 

at  a  temperature  of  from  1525  to  1600  degrees  F.  and  permit- 
ted to  cool  slowly,  after  which  they  are  reheated  to  from  1650 
to  1700  degrees  F.  and  quenched  in  oil,  and  again  reheated  for 
tempering  to  from  350  to  550  degrees  F.  and  permitted  to  cool 
slowly. 

In  the  annealed  state,  chrome-vanadium  steels  have  practi- 
cally the  same  strength  as  nickel  steels  with  the  same  carbon 
content.  When  heat-treated,  the  o.i5-per-cent  carbon  steel 
has  an  elastic  limit  of  from  50,000  to  90,000  pounds  per  square 
inch;  the  o.3o-per-cent  carbon  steel  has  an  elastic  limit  of  from 
60,000  to  150,000  pounds  per  square  inch;  the  o.4o-per-cent 
carbon  steel  has  an  elastic  limit  of  from  65,000  to  175,000  pounds 
per  square  inch.  The  o.45-per-cent  carbon  chrome- vanadium 
steel,  when  heat-treated,  has  an  elastic  limit  of  from  150,000  to 
200,000  pounds  per  square  inch;  and  the  o.5o-per-cent  carbon 
steel  may  reach  an  elastic  limit  of  225,000  pounds  per  square 
inch.  The  great  strength  of  these  steels,  however,  is  obtained 
by  a  sacrifice  of  elongation,  the  elongation  in  the  higher  carbon 
steels  being  only  from  2  to  10  per  cent. 

Chrome-vanadium  steels  are  used  when  a  better  material 
than  nickel  steel  is  required.  They  are  easily  forged  and  are 
not  as  difficult  to  machine  as  chrome-nickel  steels.  They  are 
preferably  made  in  crucible  or  electric  furnaces,  although  open- 
hearth  chrome-vanadium  steel  is  also  used.  The  open-hearth 
steel,  however,  is  not  uniform,  and  for  springs  of  the  best  quality 
there  is  nothing  superior  to  a  crucible  chrome-vanadium  steel. 

Nickel-chromium  Steel.  —  Nickel-chromium  steels  are  used 
to  a  considerable  extent  in  the  automobile  industries,  and  also 
for  armor-plate  steel.  The  steel  has  remarkable  qualities  with 
regard  to  strength,  hardness,  and  ductility.  The  nickel-chro- 
mium steel  as  used  in  the  industries  is  divided  into  three  dis- 
tinct classes  —  low,  medium,  and  high  nickel-chromium  steels. 
In  the  low  nickel-chromium  steels,  the  percentage  of  nickel 
varies  from  i.oo  to  1.50  per  cent,  and  that  of  chromium,  from 
0.30  to  0.75  per  cent.  In  the  medium  nickel-chromium  steels, 
the  percentage  of  nickel  is  about  1.75  per  cent,  and  that  of  chro- 
mium, about  i.oo  per  cent.  In  the  high  nickel-chromium  steels, 


STRUCTURAL  STEELS  273 

the  percentage  of  nickel  is  about  3.5  per  cent,  and  that  of  chro- 
mium, 1.5  per  cent.  The  carbon  content  in  either  of  these 
steels  may  vary  from  0.15  to  0.50  per  cent,  according  to  the  uses 
for  which  the  steels  are  intended.  The  manganese  content 
should  be  about  0.65  per  cent  in  the  "low"  steels,  and  0.45  per 
cent  in  the  " medium"  and  "high"  steels,  and  the  content  of 
either  phosphorus  or  sulphur  must  not  exceed  0.04  per  cent  in 
any  of  the  steels.  The  low  nickel-chromium  steels  with  carbon 
up  to  0.20  per  cent  are  mainly  intended  for  casehardening,  while 
those  with  from  0.25  to  0.40  per  cent  of  carbon  are  used  for  general 
machine  parts  requiring  strength  and  toughness.  When  the 
carbon  content  is  as  high  as  0.45  or  0.50  per  cent,  the  steel  may 
be  used  for  gears.  Medium  nickel-chromium  steels  are  used  for 
practically  the  same  purposes  as  low  nickel-chromium  steels. 

The  high  nickel-chromium  steels  are  used  for  parts  of  impor- 
tant character,  where  unusual  strength  is  required.  The  qualities 
with  a  low  carbon  content  are  used  for  casehardening  purposes; 
those  with  a  medium  carbon  content,  for  heat-treated  parts 
generally;  and  those  with  from  0.45  to  0.50  per  cent  of  carbon, 
for  gears  where  extreme  strength  and  hardness  are  required,  the 
carbon  content  being  sufficiently  high  to  cause  the  material  to 
harden,  when  quenched,  without  being  casehardened.  This 
steel  is  difficult  to  machine  and  forge.  Before  machining,  it 
must  be  annealed,  and  when  forged  it  must  be  kept  at  a  high, 
almost  plastic,  heat,  and  should  not  be  hammered  nor  worked 
at  ordinary  forging  temperatures.  At  the  same  time,  too  high  a 
temperature  must  be  avoided  in  order  not  to  injure  the  steel. 

When  low  and  medium  nickel-chromium  steels  are  casehard- 
ened, the  following  process  should  be  adopted:  Carburize  at  a 
temperature  between  1650  and  1700  degrees  F.  and  cool  slowly 
in  the  carburizing  material;  then  reheat  to  from  1450  to  1525 
degrees  F.  and  quench;  and  reheat  again  to  from  1300  to  1400  de- 
grees F.  and  quench.  Finally  temper  at  from  200  to  500  degrees 
F.  and  cool  slowly.  When  high  nickel-chromium  steel  is  case- 
hardened,  practically  the  same  procedure  should  be  followed, 
except  that  the  first  reheating  should  be  at  a  temperature  of 
about  50  degrees  less  than  that  just  specified. 


274  IRON  AND   STEEL 

The -heat- treatment  to  which  low  and  medium  nickel-chro- 
mium steels  should  be  subjected  in  order  to  increase  the  strength 
when  they  contain  0.40  per  cent  or  less  of  carbon  is  as  follows: 
Heat  to  from  1500  to  1550  degrees  F.  and  quench,  and  then  re- 
heat to  from  600  to  1 200  degrees  F.  and  cool  slowly.  A  double 
reheating  treatment  may  also  be  employed  as  follows:  Heat 
to  from  1500  to  1550  degrees  F.  and  quench,  reheat  to  from  1300 
to  1400  degrees  F.  and  quench,  and  finally  reheat  to  from  600 
to  1 200  degrees  F.  and  cool  slowly.  This  latter  treatment  is 
also  suitable  for  low  and  medium  nickel-chromium  steels  con- 
taining from  0.45  to  0.50  per  cent  of  carbon. 

The  high  nickel-chromium  steels  containing  from  0.20  to  0.35 
per  cent  of  carbon  may  be  heat-treated  in  a  similar  manner  to 
the  low  and  medium  nickel-chromium  steels,  except  that  the 
heating  temperature  should  be  in  every  cass  about  50  degrees 
F.  less  than  for  these  steels.  The  o.45-per-cent  high  nickel- 
chromium  steel  should  be  heat-treated  as  follows:  Hold  at  a 
temperature  of  from  1475  to  1525  degrees  F.  for  half  an  hour 
and  then  cool  slowly;  reheat  to  from  1450  to  1500  degrees  F. 
and  quench  in  oil;  and  finally  reheat  for  tempering  to  from  250 
to  550  degrees  F.  and  cool  slowly. 

Natural  Alloy  Steel.  —  Natural  alloy  steel  is  a  nickel-chro- 
mium steel  deriving  its  name  from  the  fact  that  the  steel  is  not 
obtained  by  adding  nickel  and  chromium  to  steel,  but  is  manu- 
factured from  an  ore  in  which  nickel  and  chromium  are  alloyed 
with  iron  by  nature.  These  natural  alloy  steels  contain  from  i.o 
to  1.5  per  cent  of  nickel,  from  0.2  to  0.7  per  cent  of  chromium, 
from  0.15  to  1.5  per  cent  of  carbon,  and  from  0.5  to  0.8  per  cent 
of  manganese.  These  steels  are  made  by  the  open-hearth  process 
and  are  largely  used  in  the  manufacture  of  automobile  parts. 
Those  being  low  in  carbon  are  suitable  for  casehardening  and 
also  for  cold-drawing,  for  seamless  tubes,  drop-forgings,  etc. 
The  grades  having  high  percentages  of  carbon  are  suitable  for 
axles,  transmission  gears,  etc. 

Copper  Alloy  Steel.  —  A  steel  containing  from  0.30  to  0.35 
per  cent  of  carbon,  from  1.50  to  1.80  per  cent  of  nickel,  and  from 
0.50  to  0.80  per  cent  of  copper  has  been  found  equal  in  its  proper- 


STRUCTURAL  STEELS 


275 


ties  to  a  3-per-cent  nickel  steel,  and  is  a  suitable  substitute  for 
this  steel,  the  composition  of  which  would  make  it  more  expen- 
sive. If  0.50  per  cent  of  chromium  is  added  to  the  alloy  men- 
tioned, the  properties  of  the  steel  will  equal  those  of  nickel- 
chromium  steel  having  i  per  cent  of  chromium  and  3  per  cent  of 
nickel;  hence,  the  influence  of  a  small  percentage  of  copper  is 
very  marked.  It  is  claimed  that  this  alloy  steel,  without  chro- 
mium, may  be  expected  after  heat-treatment  to  have  an  elastic 
limit  of  65,000  pounds  per  square  inch,  and  with  0.50  per  cent  of 
chromium,  to  have  an  elastic  limit  of  110,000  pounds  per  square 
inch  with  an  elongation  of  17  per  cent  and  a  reduction  of  area 
of  44  per  cent.  It  is  possible  that  in  the  future  this  steel  will 
be  more  generally  used,  if  it  is  found  that  the  claims  made  for 
it  are  backed  up  by  practical  experience. 


CHAPTER  XII 
HIGH-SPEED   STEEL 

IN  the  manufacture  of  steel,  there  are  two  distinct  branches 
of  work  which  have  been  referred  to  in  preceding  chapters.  One 
is  the  production  of  steel  suitable  for  use  in  the  construction 
of  machinery,  buildings,  bridges,  and  an  endless  variety  of  other 
things  which  are  essential  to  modern  industrial  life.  The  second 
branch  of  the  steel  industry  is  in  producing  steels  which  may 
be  used  in  making  the  tools  required  for  cutting  and  otherwise 
forming  the  various  parts  that  enter  into  the  different  kinds  of 
machines  and  structures.  The  steels  which  (when  properly 
heat-treated)  are  capable  of  cutting  other  steels  or  parts  made  of 
either  wrought  iron  or  cast  iron  constitute  a  very  important 
class,  and  this  chapter  deals  with  some  of  the  wonderful  devel- 
opments which  have  been  made  in  the  manufacture  of  such 
steels.  When  ordinary  tool  or  carbon  steel  is  used  for  cutting 
metals  such  as  cast  iron  or  steel,  if  the  speed  or  rate  at  which  the 
cutting  is  done  exceeds  a  certain  amount,  the  excessive  heat 
generated  by  the  friction  at  the  cutting  end  of  the  tool  causes 
the  steel  to  lose,  to  some  extent  at  least,  the  hardness  obtained 
as  a  result  of  heat- treatment;  consequently,  the  cutting  edge  is 
worn  away  and  the  tool  no  longer  cuts  effectively. 

The  discovery  of  a  steel  which  is  commonly  known,  at  the 
present  time,  as  " high-speed  steel,"  marked  a  new  epoch  in 
the  machine  building  field.  High-speed  steel,  as  its  name  im- 
plies, is  capable  of  cutting  metal  at  much  higher  speeds  than 
ordinary  carbon  steel.  The  result  is  that  metal  can  be  removed 
much  more  rapidly  in  connection  with  machining  operations  such 
as  turning,  planing,  milling,  drilling,  etc.  When  using  plain 
carbon  steel,  the  temperature  of  the  cutting  end  must  be  kept 
below  500  or  550  degrees  F.,  but  high-speed  steels  retain  sufficient 
hardness  for  cutting  metals  even  when  the  end  is  heated  to  a 

276 


HIGH-SPEED  STEEL  277 

dull  red  or  to  uoo  or  1200  degrees  F.  Because  of  this  fact, 
such  steel  is  said  to  possess  the  property  of  red  hardness. 

High-speed  steel  has  proved  to  be  so  much  superior  to  carbon 
steel,  espscially  for  rapid  metal-cutting  operations,  that  it  has 
revolutionized  machine  shop  practice.  The  introduction  of 
this  steel  also  made  it  necessary  to  re-design  machine  tools 
generally,  so  that  they  could  withstand  the  greatly  increased 
stresses  imposed  upon  them  as  a  result  of  high-duty  operation 
made  possible  by  the  improved  cutting  tools.  Some  of  the 
more  important  facts  relating  to  the  discovery  of  the  "self- 
hardening  steel"  which  preceded  what  is  now  known  as  high- 
speed steel  will  be  referred  to  and  then  the  influence  of  different 
elements  and  the  general  characteristics  of  steels  of  this  class 
will  be  referred  to. 

Origin  of  Self -hardening  Steel.  —  The  origin  of  modern  high- 
speed steels  may  be  traced  back  to  a  wonderful  discovery  made 
by  Robert  F.  Mushet  in  1868.  Experiments  were  being  made 
with  the  use  of  manganese  in  the  production  of  Bessemer  steel, 
and  at  first  there  was  no  idea  of  improving  tool  steel.  During 
these  experiments  it  was  discovered  that  one  of  the  bars  of  steel 
had  the  property  of  hardening  after  being  heated,  without 
quenching  or  cooling  it  rapidly  in  the  manner  required  to  harden 
carbon  steel.  This  steel,  which  was  afterwards  known  as  mushet 
or  self-hardening  steel,  was  found  to  contain  tungsten.  The 
ne  tvly  discovered  steel  which  possessed  the  property  of  hardening 
when  allowed  to  cool  slowly  without  quenching,  proved  to  be 
harder  than  steel  which  was  quenched  in  the  usual  way.  This 
discovery  of  self-hardening  or  air-hardening  steel,  as  it  was  also 
called,  led  to  numerous  experiments  with  different  elements  in 
various  combinations  and,  as  a  result,  an  alloy  steel  was  ob- 
tained which  was  superior  to  carbon  steel  for  rapid  machining 
operations.  The  discovery  was  made  later  that  the  quality  of 
the  steel  could  be  improved  if  the  cutting  end  were  reheated  and 
cooled  in  an  air  blast,  instead  of  being  allowed  to  cool  by  simply 
exposing  the  heated  steel  to  the  atmosphere.  An  analysis  of  a 
typical  mushet  self-hardening  steel  showed  the  following  com- 
position: Tungsten,  5.441  per  cent;  chromium,  0.398  per  cent; 


278  IRON  AND   STEEL 

carbon,  2.15  per  cent;  manganese,  1.578  per  cent;  silicon,  1.044 
per  cent. 

Cutting  Speeds  Obtained  with  Mushet  Steel.  —  The  self- 
hardening  steel  was  at  first  regarded  somewhat  as  a  curiosity, 
but  gradually  it  was  found  that  it  had  superior  qualities  and  that 
it  could  be  used  for  cutting  hard  forgings  and  castings  which  were 
difficult  to  cut  with  carbon  steel  tools.  It  was  some  time  after 
the  introduction  of  self-hardening  steel  before  its  advantage  as 
a  means  of  increasing  production  was  realized.  In  1894,  a  series 
of  experiments  was  conducted  by  F.  W.  Taylor  in  order  to  de- 
termine the  relative  cutting  speeds  of  mushet  and  carbon  steel 
tools.  These  experiments  showed  that  self -hardening  steel  made 
it  possible  to  increase  the  cutting  speed  from  41  to  47  per  cent 
(as  compared  with  carbon  steel)  when  cutting  a  hard  forging  of 
about  the  quality  of  tire  steel,  and  when  cutting  softer  steels,  a 
gain  of  nearly  90  per  cent  was  secured.  A  second  discovery  was 
made  in  regard  to  the  use  of  a  heavy  stream  of  water  on  the  nose 
of  a  mushet  or  other  self-hardening  tool  which  resulted  in  a 
gain  of  about  30  per  cent  in  the  cutting  speed.  These  experi- 
ments showed  that  mushet  steel  was  not  only  good  for  cutting 
unusually  hard  metals,  but  that  its  greatest  field  of  usefulness 
was  in  increasing  the  cutting  speeds  and  production  in  connection 
with  all  kinds  of  metal-cutting  operations.  After  these  experi- 
ments had  been  made,  the  use  of  self-hardening  steels  increased 
very  rapidly,  until,  as  mentioned  before,  these  steels  and  others 
of  superior  quality  developed  later  brought  about  a  great  change 
in  machine  shop  practice,  especially  in  regard  to  the  rate  at 
which  metal  could  be  removed. 

Effect  of  Heat-treatment  on  Durability.  —  About  twenty-five 
years  after  the  discovery  of  mushet  or  self-hardening  steel,  a 
second  very  important  discovery  was  made  by  F.  W.  Taylor  and 
M.  White,  in  connection  with  experiments  both  with  mushet  and 
other  self-hardening  steels  which  had,  at  that  time,  been  pro- 
duced. -  This  second  discovery  was  a  method  of  heat-treating 
self -hardening  steels  which  would  greatly  increase  the  durability 
of  cutting  tools  and  enable  them  to  retain  an  effective  cutting 
edge  at  much  higher  cutting  speeds  than  were  possible  with  tools 


HIGH-SPEED   STEEL  279 

heat-treated  by  methods  formerly  employed.  It  was  found  that 
self-hardening  steels  could  be  given  the  quality  which  was  re- 
ferred to  as  red  hardness,  by  heating  the  steel  to  a  hardening 
temperature  much  higher  than  was  required  for  ordinary  car- 
bon steels.  In  fact,  the  preferable  hardening  temperature 
proved  to  be  very  near  to  the  melting  point  of  the  steel  —  a 
temperature  which  would  ruin  carbon  tool  steel.  The  steel  sub- 
jected to  this  high  heat-treatment  was  so  much  superior  to  the 
self-hardening  steel  heat-treated  in  the  usual  way,  that  it  was 
known  as  ''high-speed  steel"  as  it  enables  cutting  speeds  to  be 
increased  greatly. 

Many  have  supposed  that  the  greater  durability  of  the  self- 
hardening  steels  and  of  the  high-speed  steels  developed  later  is 
due  to  an  extreme  degree  of  hardness,  but  this  is  not  the  case. 
The  fact  is  that  steels  of  this  general  class  are  little,  if  any, 
harder  than  carbon  steel,  and  heating  the  steel  close  to  the  melt- 
ing point  does  not  result  in  an  extreme  degree  of  hardness. 
This  method  of  heat-treatment,  however,  does  give  a  self-hard- 
.  ening  or  high-speed  steel  a  remarkable  'property  of  retaining  its 
hardness,  even  when  it  has  been  heated  red  hot  as  the  result  of 
the  heat  generated  by  cutting.  When  hardening  carbon  steels, 
the  temperature  ordinarily  varies  from  1400  to  1600  degrees  F., 
but  in  order  to  secure  the  best  results  with  high-speed  steel  it 
must  be  heated  to  temperatures  usually  varying  from  1800  to 
2300  degrees  F. 

Taylor- White  Method  of  Heat-treatment.  —  The  exact  method 
of  heat- treatment  by  the  Taylor- White  process  is  as  follows: 
The  nose  or  cutting  end  of  the  forged  tool  is  heated  slowly  and 
uniformly  to  a  bright  cherry-red,  or  to  1500  degrees  F.,  allowing 
plenty  of  time  so  that  the  heat  penetrates  thoroughly  to  the  cen- 
ter of  the  tool.  From  this  point  on,  the  tool  is  heated  as  rapidly 
as  practicable  in  an  intensely  hot  fire  until  the  nose  begins  to 
soften.  The  whole  end  of  the  tool  from  the  heel  to  the  upper  or 
lip  surface  should  be  uniformly  heated  to  this  same  high  heat. 
If  the  fire  is  hot  enough,  a  tool  having  a  2-  by  3 -inch  body  can  be 
properly  heated  in  three  minutes  from  a  bright  cherry-red  up  to 
the  maximum  heat  required,  although  it  is  difficult  to  do  this  in 


280  IRON  AND   STEEL 

the  time  mentioned  without  using  a  specially  designed  furnace. 
After  heating  the  tool  as  described,  it  should  be  cooled  rapidly 
down  to  or  below  1550  degrees  F.,  and  then  it  may  be  cooled 
either  rapidly  or  slowly  from  this  point  down  to  the  temperature 
of  the  atmosphere.  The  preferable  method  of  cooling  from  the 
high  heat  down  to  1550  degrees  F.  is  by  plunging  the  tool  into  a 
bath  of  red-hot  molten  lead  which  is  below  a  temperature  of 
1550  degrees  F.  It  is  very  important  to  avoid  any  increase  of 
temperature  during  the  cooling  period,  as  any  temporary  rise 
of  temperature  will  injure  the  tool  unless  this  increase  occurs  at 
temperatures  below  1240  degrees  F.  After  a  tool  has  received 
the  "high  heat-treatment,"  it  is  subjected  to  a  second  or  "low 
heat- treatment"  which  consists  of  reheating  to  a  temperature 
somewhere  between  700  and  1240  degrees  F.  A  lead  bath  is 
preferable  for  this  second  heat-treatment  which  should  be  for  a 
period  of  about  five  minutes.  A  temperature  of  about  1150 
degrees  F.  is  liable  to  give  the  best  results.  The  tool  may  be 
cooled  either  rapidly  or  slowly  to  the  temperature  of  the  air. 

When  high-speed  steel  tools  must  be  heated  in  an  ordinary 
forge,  a  deep  bed  either  of  coke  or  of  first-class  soft  coal  is  recom- 
mended. Several  tools  should  be  laid  with  their  ends  at  a  slight 
distance  from  the  hottest  part  of  the  fire,  so  that  they  are  being 
heated  while  the  temperature  of  the  fire  is  increasing  to  the 
proper  degree.  Then  the  tools  are  heated  one  at  a  time  over 
the  hottest  section  ot  the  fire  and  as  rapidly  as  possible  up  to  a 
temperature  just  below  the  melting  point.  In  order  to  secure 
a  more  uniform  heating,  the  tool  should  be  repeatedly  turned 
over.  As  soon  as  each  tool  receives  its  high  heat,  the  cutting 
end  is  placed  under  a  heavy  air  blast  and  is  allowed  to  cool  to  the 
temperature  of  the  atmosphere  before  being  removed. 

Production  of  High-speed  Steel.  —  High-speed  steel  may  be 
produced  either  by  means  of  the  crucible  process  or  in  the  elec- 
tric furnace.  The  methods  of  making  carbon  and  high-speed 
steel  by  the  crucible  process  are  practically  the  same  so  far  as 
equipment  and  general  procedure  is  concerned.  The  principal 
difference  is  in  the  materials  which  are  placed  in  the  crucible 
and  which  control  the  composition  of  the  steel.  The  different 


HIGH-SPEED   STEEL 


281 


materials  required,  such  as  tungsten,  charcoal  for  supplying  the 
carbon,  chromium,  or  whatever  elements  are  to  be  combined 
with  the  iron,  are  proportioned  and  measured  very  carefully, 
so  that  the  composition  of  the  steel  will  conform  to  the  formula 
which  has  been  adopted.  These  different  elements  should  pref- 
erably be  placed  in  the  bottom  of  the  crucible  and  beneath  the 
small  pieces  of  iron. 

The  ores  from  which  tungsten,  molybdenum,  chromium,  etc., 
are  obtained  are  reduced  in  the  electric  furnace  and  either  to  the 
metallic  state  or  to  a  ferro-alloy.  Ferrotungsten,  which  is  an 


Fig.  i.     High-speed  Steel  Turning  Tool  at  Work 

alloy  o£  iron  and  tungsten,  contains  from  50  to  85  per  cent  of 
tungsten.  It  may  be  produced  directly  from  tungsten-bearing 
ores  more  easily  than  metallic  tungsten,  and  it  is  claimed  that 
less  tungsten  is  lost  when  introduced  into  the  steel  as  ferrotung- 
sten.  Pure  iron  free  from  phosphorus,  sulphur,  and  other  im- 
purities is  very  essential.  Some  steel-makers  consider  it  neces- 
sary to  use  Swedish  or  Dannemora  iron  for  producing  the  best 
grades  of  high-speed  steel,  because  of  the  small  percentage  of  im- 
purities found  in  these  irons.  Other  steel-makers  contend  that 
native  muck-bar  iron  meets  all  the  requirements.  In  the  pro- 

18* 


282  IRON  AND   STEEL 

duction  of  a  first-class  high-speed  steel,  careful  tests  and  inspec- 
tion are  necessary  during  the  process  of  manufacture  to  make 
sure  that  the  steel  conforms  to  the  required  composition  and  to 
guard  against  defects  or  flaws. 

Effect  of  Different  Elements  in  High-speed  Steels. —  The 
effect  of  different  elements  entering  into  the  composition  of 
high-speed  steels  and  the  reasons  why  tungsten,  chromium,  and 
other  elements  give  steels  of  this  class  such  unusual  properties 
will  be  more  apparent  by  considering  first  the  changes  that  occur 
in  the  hardening  of  ordinary  carbon  steel.  As  explained  in 
Chapter  V  in  connection  with  the  microscopic  study  of  heat- 
treated  steels,  the  pearlite,  ferrite,  and  cementite  of  annealed 
steels  are  replaced  by  other  constituents  when  the  steel  is  sub- 
jected to  the  heat-treatment  required  for  hardening  and  temper- 
ing. Annealed  steel  containing  approximately  0.90  per  cent  of 
carbon  is  composed  entirely  of  pearlite.  Incidentally,  the  com- 
position of  most  of  the  steels  of  which  cutting  tools  are  made  is 
largely  pearlite  before  the  steel  is  hardened.  Steels  that  con- 
tain less  than  0.90  per  cent  of  carbon  have,  in  addition  to  pearlite, 
ferrite,  which  increases  as  the  carbon  content  decreases.  On 
the  other  hand,  if  there  is  more  than  0.90  per  cent  of  carbon,  the 
steel  is  composed  of  pearlite  and  cementite.  Now  if  any  of  these 
steels  are  heated  sufficiently,  the  elements  referred  to  change  to 
austenite.  If  the  annealed  steel  has  0.90  per  cent  of  carbon  and 
is  all  pearlite,  the  change  to  austenite  occurs  at  about  1355 
degrees  F.,  but  the  effect  of  either  ferrite  or  cementite  is  to  in- 
crease the  temperature  at  which  conversion  to  austenite  occurs. 
After  a  steel  has  been  heated  sufficiently  to  change  it  to  the  aus- 
tenitic  condition,  some  of  this  austenite  may  remain  after  the 
steel  has  been  cooled  to  the  temperature  of  the  atmosphere,  al- 
though this  necessitates  very  rapid  cooling.  Were  it  not  for  the 
carbon  element,  the  austenite  could  not  be  retained  even  though 
the  rate  of  cooling  were  extremely  rapid,  the  effect  of  carbon  being 
to  obstruct  the  change  and  assist  in  keeping  the  steel  in  the  aus- 
tenitic  condition.  The  carbon,  therefore,  acts  as  a  fixing  agent, 
and  if  there  is  a  carbon  content  of  over  i  per  cent,  the  austenite 
may  be  fixed  in  cold  steel,  provided  the  steel  is  heated  to  a  white 


HIGH-SPEED  STEEL  283 

heat  and  is  then  cooled  very  rapidly  by  using  a  quenching  bath 
such  as  iced  brine,  which  is  below  the  freezing  point  of  water. 

The  ordinary  methods  of  heat- treatment  produce  martensite 
which  is  harder  than  austenite.  Martensite  is  formed  between 
the  change  from  austenite  to  pearlite,  the  order  being  from 
austenite  to  martensite,  as  the  steel  cools.  The  change  from 
austenite  to  martensite  is  difficult  to  prevent,  because  it  occurs 
rapidly,  the  change  from  martensite  to  pearlite  being  relatively 
slow.  While  the  hardness  of  martensite  is  a  desirable  quality, 
steel  in  this  condition  is  too  brittle  for  most  purposes,  and  it  is 
necessary  to  sacrifice  the  hardness  by  tempering,  which  toughens 
the  steel  and  makes  it  better  able  to  withstand  shocks.  The 
practical  effect  of  tempering  is  to  reduce  the  martensite  or  "let 
it  down"  toward  the  pearlite  condition.  The  formation  of 
troostite  (which  occurs  between  martensite  and  pearlite)  and 
of  sorbite  as  the  result  of  tempering  was  explained  in  Chapter  V. 

Influence  of  Carbon  on  High-speed  Steels.  —  Among  the 
elements  found  in  high-speed  steels  are  carbon,  tungsten,  molyb- 
denum, chromium,  vanadium,  manganese,  uranium,  and  silicon. 
These  various  elements  are,  of  course,  used  in  a  great  variety  of 
combinations  and  proportions,  and  in  many  cases  the  exact 
composition's  kept  secret  by  the  steel-maker.  The  carbon  con- 
teat  may  vary  from  0.4  to  2  per  cent  or  more.  At  one  time,  most 
high-speed  steels  had  a  carbon  content  varying  between  i  and 
2  per  cent,  although  later  many  steel-makers  reduced  this 
amount  and  high-speed  steels  having  less  than  i  per  cent  of 
carbon  are  now  common.  Experiments  have  indicated  that 
when  a  high-speed  steel  is  hardened  by  the  method  previously 
referred  to,  of  heating  almost  to  the  melting  point  and  then 
rapidly  cooling  in  a  strong  air  blast,  a  carbon  content  varying 
from  0.4  to  0.9  per  cent  gives  the  best  results.  When  there  is 
more  carbon,  considerable  difficulty  is  experienced  in  forging  the 
steel,  and  its  cutting  efficiency  is  also  less.  The  steel  is,  in  addi- 
tion, more  brittle  and  tends  to  break,  particularly  if  there  is 
unequal  or  intermittent  cutting.  The  effect  of  carbon  in  high- 
speed steel  is  to  increase  the  time  required  for  the  change  from 
the  austenitic  to  the  pearlitic  condition. 


284  IRON  AND   STEEL 

Influence  of  Manganese.  —  Manganese,  like  carbon,  delays 
the  change  from  austenite  to  pearlite,  but  it  acts  in  a  different 
way.  The  effect  of  carbon  is  to  obstruct  the  change,  whereas 
manganese  causes  it  to  occur  at  a  lower  temperature,  and  as  the 
manganese  content  increases,  the  temperature  at  which  the 
change  takes  place  decreases.  The  result  is  that,  when  there  is 
about  12  per  cent  of  manganese,  the  change  to  the  pearlitic 
condition  does  not  occur  even  when  the  steel  is  cold;  conse- 
quently, such  a  steel  is  self-hardening  and  even  though  it  is 
annealed,  austenite  and  ordinarily  martensite  remain  fixed. 
The  change  from  austenite  to  martensite  occurs  rapidly  and,  for 
this  reason,  is  difficult  to  prevent.  Manganese  steel  which  cools 
slowly  will  be  more  or  less  martensitic,  whereas,  if  it  is  cooled 
rapidly  from  a  white  heat,  the  austenitic  condition  will  be  ob- 
tained. Such  steel  will  not  be  as  hard  as  that  which  is  marten- 
sitic, but  it  will  not  be  brittle  like  the  latter.  In  fact,  steel  in  the 
austenitic  condition  is  tough,  but  the  elastic  limit  is  low.  Man- 
ganese steel  is  not  suitable  for  cutting  tools,  because  the  edge  of 
the  tool  will  not  withstand  the  severe  service  to  which  metal- 
cutting  tools  are  subjected. 

Influence  of  Tungsten.  —  Tungsten  is  a  very  important  ele- 
ment in  high-speed  steels  and  is  utilized  very  extensively  in  the 
manufacture  of  steels  of  this  class.  Tungsten  is  another  element 
which  delays  the  change  from  austenite  to  pearlite.  The  effect 
is  so  pronounced  that  the  change  will  be  prevented  entirely  if 
there  is  7  per  cent  or  more  of  tungsten,  even  though  the  heated 
steel  is  allowed  to  cool  slowly  in  the  air.  For  this  reason,  it  is 
necessary  to  cool  a  tungsten  steel  at  an  extremely  slow  rate  in 
order  to  anneal  it  or  to  change  it  to  the  pearlite  condition.  The 
reason  why  high-speed  steels  in  general  can  be  heated  consider- 
ably as  the  result  of  high  cutting  speeds  and  excessive  friction 
is  that  some  element  (or  combination  of  elements),  such,  for 
example,  as  tungsten,  so  changes  the  characteristics  of  the  steel 
that  the  increase  of  temperature  does  not  reduce  it  to  the  pearlitic 
stage,  the  same  as  with  ordinary  carbon  steel.  The  martensite 
in  carbon  steel  will  not  remain  fixed  if  the  steel  is  heated  beyond 
a  certain  point,  but  if  there  is  sufficient  tungsten  in  the  com- 


HIGH-SPEED  STEEL 


285 


position,  the  martensite  remains  even  though  the  temperature 
is  raised  above  that  required  for  tempering.  The  natural  tend- 
ency is  for  the  martensite  to  change  to  troostite  and  finally  back 


Fig.  2.     Planing  with  a  High-speed  Steel  Tool 

to  pearlite,  or  to  the  condition  normal  to  annealed  steel.  The 
effect  of  tungsten  to  resist  change  from  the  martensitic  condition 
explains  why  steel  may  have  the  property  of  red  hardness. 

Experiments  made  with  a  tungsten  content  varying  from  9  to 
27  per  cent  showed  that  from  9  to  16  per  cent  the  steel  becomes 


286  IRON  AND   STEEL 

very  brittle,  but  the  cutting  efficiency  greatly  increases.  No 
better  results,  however,  were  obtained  by  increasing  the  tungsten 
content  to  more  than  16  per  cent.  When  the  amount  of  tung- 
sten varied  between  18  and  27  per  cent,  the  steel  lost  its  brittle- 
ness  and  became  softer  and  tougher.  While  this  latter  steel  did 
not  stand  up  so  well,  it  did  have  the  property  of  cutting  very 
"cleanly."  The  composition  of  tungsten  steel  specified  for  the 
Navy  Department  is  as  follows  (when  two  figures  are  given 
these  represent  minimum  and  maximum  percentages):  Tung- 
sten, from  1 6  to  20  per  cent;  carbon,  from  0.55  to  0.75  per  cent; 
chromium,  from  2.50  to  5  per  cent;  manganese,  from  0.05  to 
0.30  per  cent;  phosphorus,  0.015  per  cent;  silicon,  0.30  per  cent; 
sulphur,  0.02  per  cent;  vanadium,  from  0.35  to  1.5  per  cent. 
Iron  is  the  element  which  represents  the  remaining  percentage 
in  the  composition  of  the  steel. 

Influence  of  Chromium.  —  The  effect  of  chromium  is  similar 
to  carbon  in  that  it  obstructs  the  natural  tendency  of  heated 
steel  to  change  from  the  austenitic  to  the  pearlitic  condition. 
Experiments  which  showed  that  the  best  carbon  content  varied 
from  0.4  to  0.9  per  cent  were  followed  by  other  tests  to  deter- 
mine the  effect  of  chromium  varying  from  i  to  6  per  cent.  A 
low  percentage  of  chromium  was  found  to  produce  a  tough  steel 
which  was  very  satisfactory  for  cutting  cast  iron  or  comparatively 
soft  steels,  but  this  steel  was  not  very  effective  when  applied  to 
harder  materials.  For  the  latter  class  of  work,  steel  having  a 
larger  amount  of  chromium  was  found  to  be  preferable,  because 
the  increase  of  chromium  produces  a  harder  steel.  In  order  to 
obtain  the  best  results,  however,  it  is  necessary  to  decrease  the 
carbon  in  the  steel  as  the  chromium  content  is  increased.  Chro- 
mium and  carbon  will  not  produce  a  self-hardening  steel,  al- 
though if  there  is  approximately  i  per  cent  of  carbon  and  i  or 
2  per  cent  of  chromium,  such  steel  becomes  very  hard  when 
cooled  rapidly,  and  the  hardness  resulting  from  the  chromium 
causes  the  steel  to  be  less  brittle  than  plain  carbon  steel.  If 
toughness  is  the  desirable  quality,  there  should  be  about  1.5  per 
cent  of  chromium,  whereas,  if  an  extremely  hard  steel  is  desired, 
the  chromium  content  may  be  increased  to  from  4  to  6  per  cent. 


HIGH-SPEED  STEEL  287 

While  a  chromium-carbon  steel  is  not  self-hardening,  chromium 
combined  with  manganese  produces  a  steel  which  has  the  self- 
hardening  property.  The  manganese  content  in  this  case  is 
only  a  few  per  cent  and  very  much  less  than  is  found  in  man- 
ganese steel. 

Influence  of  Vanadium.  —  Many  of  the  high-speed  steels  now 
manufactured  contain  from  0.75  to  i  per  cent  of  vanadium,  al- 
though when  this  element  was  first  used  the  content  ordinarily 
varied  from  about  0.2  to  0.3  per  cent.  An  increase  in  the  amount 
of  vanadium,  however,  was  found  to  give  better  results.  Tests 
made  to  determine  the  influence  of  vanadium  on  the  durability  of 
steel  at  different  cutting  speeds  showed  that  a  tool  steel  con- 
taining 0.3  per  cent  of  vanadium  may  have  a  10  per  cent  higher 
cutting  speed  than  a  steel  without  vanadium.  By  increasing 
the  vanadium  content  to  0.6  per  cent,  the  cutting  speed  was 
increased  20  per  cent,  and  with  0.9  per  cent  of  vanadium,  an 
increase  of  30  per  cent  in  the  cutting  speed  was  practicable. 
Another  series  of  tests  in  which  the  same  cutting  speed  was 
maintained  showed  that  the  time  between  grindings  was  doubled 
in  the  case  of  an  o.3-per-cent  vanadium  steel,  quadrupled  with 
an  o.6-per-cent  vanadium  steel,  and  0.9  per  cent  increased  the 
period  between  grindings  eight  times. 

Influence  of  Molybdenum.  —  The  effect  of  molybdenum  on 
steel  is  similar  to  that  of  tungsten.  One  of  the  noteworthy 
properties  of  molybdenum  steels  is  that  they  do  not  require 
such  a  high  temperature  for  hardening  as  is  necessary  in  the  case 
of  tungsten  steels.  The  latter  are  commonly  heated  to  2200 
or  2300  degrees  F.,  whereas  a  molybdenum  steel  is  injuriously 
affected  if  heated  much  above  1800  degrees  F.  The  cutting 
efficiency  of  a  high  tungsten  steel  is  increased  somewhat  by  the 
addition  of  from  0.5  to  3  per  cent  of  molybdenum,  although  the 
advantage  is  not  in  proportion  to  the  increase  in  cost. 

Influence  of  Silicon.  —  High-speed  steels  may  contain  silicon 
varying  from  a  mere  trace  up  to  4  per  cent.  The  addition  of 
silicon  up  to  about  3  per  cent  is  supposed  to  increase  the  cutting 
efficiency,  particularly  if  the  tools  are  applied  to  hard  material; 
but  higher  silicon  contents  have  the  opposite  effect  and  reduce 


288  IRON  AND   STEEL 

the  efficiency.  A  high  silicon  content  increases  the  hardness 
of  the  steel,  but  also  makes  it  brittle. 

Tungstenless  High-speed  Steel.  —  A  high-speed  steel  con- 
taining no  tungsten  whatever  has  been  produced  by  a  Sheffield 
concern  and  is  claimed  to  be  equal  in  durability  and  hardness  to 
any  high-speed  steel  containing  tungsten.  This  comparatively 
new  steel  (which  is  called  "  cobaltcrom ")  is  said  to  be  suitable 
for  making  milling  cutters,  twist  drills,  reamers,  taps,  forming 
tools,  and  screw-cutting  and  finishing  tools  in  general.  It  is 
further  claimed  that  the  endurance  of  the  steel  is  not  only  equal 
to  any  tungsten  high-speed  steel,  but  that  it  is  tougher,  pro- 
duces a  better  finish,  and  does  not  crack  in  hardening,  even  in 
the  case  of  tools  of  intricate  shape.  This  steel  is  hardened  at  a 
temperature  of  about  1830  degrees  F.,  as  compared  with  the 
higher  temperatures  of  2300  or  2400  degrees  F.  for  tungsten 
high-speed  steel.  The  specific  gravity  of  cobaltcrom  is  about 
10  per  cent  less  than  that  of  tungsten  high-speed  steel.  It 
contains  about  1.5  per  cent  of  carbon,  12.5  per  cent  of  chromium, 
and  3.5  per  cent  of  cobalt. 

Uranium  High-speed  Steel.  —  It  is  claimed  that  uranium 
possesses  powerful  deoxidizing  and  de-nitrogenizing  effects  when 
applied  to  high-speed  steel,  and  that  it  increases  the  toughness 
and  durability  of  the  steel.  The  Standard  Alloys  Co.,  Pitts- 
burg,  Pa.,  recommends  that  this  steel  be  heated  to  between 
2200  and  2300  degrees  F.,  and  if  it  is  to  be  "drawn  back,"  the 
temperature  should  be  about  900  degrees  F.  This  steel  can  be 
cooled  in  an  air  blast  or  quenched  in  oil,  but  the  former  method 
appears  preferable.  The  claim  made  for  uranium  high-speed 
steel  is  that  it  has  to  a  marked  degree  the  property  of  toughness 
and  is  capable  of  severe  duty  without  any  breaking  away  or 
crumbling  along  the  cutting  edge  of  a  properly  ground  tool. 

Semi-high-speed  Steel.  —  A  semi-high-speed  steel  may  be  de- 
fined as  a  steel  which  is  not  capable  of  withstanding  such  fast 
cutting  speeds  as  a  steel  ordinarily  designated  as  high-speed; 
the  semi-high-speed  steel,  however,  is  superior  in  the  matter  of 
cutting  speed  to  ordinary  carbon  steel.  Owing  to  the  cost  of 
high-speed  steels,  the  semi-high-speed  steel  was  produced  to 


HIGH-SPEED   STEEL  289 

meet  the  demand  for  a  cheaper  steel  which  could  be  used  just 
as  well  for  certain  purposes.  For  instance,  extremely  high  speeds 
and  heavy  cuts  are  necessarily  impracticable  for  some  operations, 
as  in  the  case  of  certain  wood-working  operations  where  a  cutter 
having  greater  durability  than  one  made  of  the  best  carbon  steel 
would  last  almost  indefinitely  and  there  is  no  good  reason  for  using 
the  more  expensive  high-speed  steel.  These  "intermediate"  or 
semi-high-speed  steels  are  practically  the  mushet  or  self-harden- 
ing steels,  although  some  appear  to  be  manganese  rather  than 
tungsten  steels.  Steel  made  according  to  the  following  com- 
position is  a  typical  example  of  the  semi-high-speed  class: 
Carbon,  1.190  per  cent;  tungsten,  7.560  per  cent;  chromium, 
3.340  per  cent;  manganese,  0.460  per  cent;  phosphorus,  0.024 
per  cent;  sulphur,  0.025  per  cent;  silicon,  0.200  per  cent. 

The  composition  of  another  semi-high-speed  steel  which  cor- 
responds more  closely  to  mushet  steel  is  as  follows:  Carbon, 
0.94  per  cent;  tungsten,  4.78  per  cent;  chromium,  0.69  per 
cent;  manganese,  0.27  per  cent;  phosphorus,  o.oi  per  cent; 
sulphur,  o.oi  per  cent;  silicon,  o.n  per  cent.  The  first  steel 
referred  to  is  somewhat  higher  in  tungsten  than  mushet  steel, 
and  the  second  is  lower  in  chromium;  both  steels  also  contain 
less  carbon  than  was  found  in  most  mushet  steels.  A  steel  which 
is  classified  as  intermediate  steel  and  has  proved  very  satisfac- 
tory for  cutting  wood  and  metals  of  moderate  hardness  and  also 
for  making  blanking  and  stamping  dies  has  the  following  com- 
position: Carbon,  1.03  per  cent;  tungsten,  0.46  per  cent;  man- 
ganese, 0.30  per  cent;  phosphorus,  0.025  per  cent;  sulphur 
0.009  Per  cent;  silicon,  0.008  per  cent.  This  is  a  dense  steel 
which  requires  very  slow  and  careful  heating  to  a  temperature 
of  about  from  1500  to  1550  degrees  F.  for  cutting  tools  and  a 
somewhat  lower  temperature  for  tools  that  must  withstand 
pressure  or  blows.  This  steel  must  be  hardened  by  quenching 
and  the  temper 'should  be  drawn  the  same  as  with  carbon  tool 
steels.  It  is  claimed  that  this  steel  is  much  tougher  than  car- 
bon tool  steel,  although  it  does  not  differ  from  the  latter  greatly. 
A  steel  which  is  designated  as  a  " finishing  steel"  and  has  given 
excellent  results  for  this  kind  of  work  contains  1.25  per  cent  of 


2  go  IRON  AND  STEEL 

carbon;  2.25  per  cent  of  tungsten;  0.28  per  cent  of  chromium; 
0.85  per  cent  of  manganese;  and  0.21  per  cent  of  silicon.  There 
are  various  other  steels  in  the  intermediate  or  semi-high-speed 
steel  class  which  have  a  tungsten  content  or  a  molybdenum 
equivalent  less  than  that  found  in  high-speed  steels. 

General  Hardening  Practice  for  High-speed  Steel.  —  The  ex- 
act heat-treatment  recommended  for  different  kinds  of  high- 
speed steel  varies  more  or  less,  and  it  is  advisable  to  follow  the 
directions  given  by  the  steel-makers.  The  general  practice 
conforms  quite  closely  to  that  previously  referred  to  in  con- 
nection with  the  Taylor  and  White  experiments;  that  is,  the 
cutting  end  is  heated  slowly  to  a  temperature  of  from  1500  to 
1800  degrees  F.  and  then  rapidly  up  to  2200  or  2300  degrees 
F.,  or  until  the  end  is  at  a  dazzling  white  heat  and  shows  signs 
of  melting.  The  tool  point  is  often  cooled  by  plunging  it  into 
a  bath  of  oil  such  as  linseed  or  cottonseed  or  by  inserting  it 
in  a  strong  blast  of  dry  air.  Taylor's  conclusion  in  regard  to 
this  point,  as  recorded  in  his  treatise  "On  the  Art  of  .Cutting 
Metals,"  is  that  cooling  the  tool  in  an  air  blast  from  the  high 
heat  will  produce  as  good  and  uniform  a  tool  as  by  any  other 
method,  outside  that  of  plunging  it  into  the  hot  lead  bath,  as 
previously  described.  It  was  claimed  that  the  more  rapid 
methods  of  cooling  either  by  plunging  into  water  or  oil  rendered 
the  tool  more  liable  to  fire  cracks  and  made  the  body  more  brittle 
and  liable  to  break  in  service,  particularly  if  there  was  any  lack 
of  uniformity  in  the  heating.  It  was  claimed  further  that  cool- 
ing in  water  or  oil  gives  no  greater  degree  of  red  hardness  than 
can  be  obtained  by  cooling  in  an  air  blast,  regardless  of  the 
chemical  composition  of  the  steel. 

When  oil  baths  are  used  for  quenching,  the  temperature  varies 
from  that  of  the  room  up  to  350  degrees  F.,  depending  upon  the 
steel  used.  These  oil  baths  are  now  used  extensively  in  prefer- 
ence to  the  air  blast  formerly  recommended  by  most  steel- 
makers. It  is  important  to  quench  the  heated  steel  very  quickly 
after  removing  it  from  the  fire  or  furnace.  In  addition  to  lin- 
seed or  cottonseed  oil  for  quenching  baths,  thin  lard  oil  and  also 
kerosene  oil  are  sometimes  used.  If  a  cutting  tool  requires  ex- 


HIGH-SPEED  STEEL  291 

tremely  hard  cutting  edges,  the  latter  are  heated  to  the  fusing 
point  and  then  the  tool  is  quenched  rapidly  in  thin  lard  oil; 
kerosene  oil  may  also  be  used  if  extreme  hardness  is  desired.  If 
kerosene  is  used,  a  galvanized  iron  tank  having  close  fitting 
covers  is  desirable  to  avoid  trouble  from  flames.  The  hardening 
methods  previously  referred  to  apply  to  tools  which  may  be 
ground  after  hardening.  When  it  is  not  practicable  to  grind 
the  cutting  edge  after  hardening,  any  melting  or  fusing  of  the 
cutting  edges  must,  of  course,  be  prevented.  The  hardening 
of  such  tools  will  be  considered  later. 

Tempering  High-speed  Steel.  —  High-speed  steel,  like  carbon 
steel,  is  often  tempered  after  hardening  to  reduce  the  brittleness 
and  to  increase  the  toughness  by  sacrificing  hardness.  Large 
heavy  tools  made  of  high-speed  steel  (such  as  are  used  on  lathes 
and  planers)  ordinarily  are  not  tempered,  because  the  cutting 
edges  are  well  supported.  The  tools,  however,  that  are  relatively 
weak  are  frequently  tempered  to  suit  the  class  of  work  for  which 
they  are  intended.  The  steel  to  be  tempered  may  be  heated  in 
an  oven  furnace  or  in  a  bath  of  oil  or  lead.  Another  approved 
method  is  to  cover  the  steel  with  clean  dry  sand  contained  in  a 
metal  pan  which  is  heated  by  a  gas  or  oil  burner,  or  in  any  con- 
venient way.  A  pyrometer  should  be  used  to  indicate  the  tem- 
perature. A  general  idea  of  the  variations  in  temperatures  for 
tempering  different  classes  of  tools  may  be  obtained  from  the 
following  data:  For  tempering  milling  cutters,  400  degrees  F.; 
for  drills  and  reamers,  440  degrees  F.,  if  the  tools  are  large,  or 
460  degrees  F.  in  the  case  of  small  sizes;  taps  and  dies  for  thread 
cutting,  490  degrees  F. 

Annealing  High-speed  Steel.  —  The  annealing  of  high-speed 
steel  is  desirable  partly  because  it  removes  the  internal  strains 
that  may  have  arisen,  due  to  hammering  and  rolling.  Annealing 
also  renders  the  steel  sufficiently  soft  to  be  machined  into  any 
desired  form  for  making  milling  cutters,  drills,  etc.  An  ad- 
ditional advantage  is  that  it  minimizes  risks  of  cracking  when  the 
steel  has  to  be  reheated  for  hardening.  In  cases  of  intricately 
shaped  tools  having  sharp-cornered  recesses,  fine  edges,  or  deli- 
cate projections,  which  are  liable  to  unequal  expansion  and 


2 Q2  IRON  AND    STEEL 

contraction,  annealing  tends  to  reduce  cracking  to  a  minimum. 
Increased  ductility  is  also  imparted  by  annealing;  this  is  espe- 
cially necessary  in  tools  subjected  to  sudden  shocks  due  to 
intermittent  cutting,  such  as  in  planing  and  slotting  or  when 
suddenly  meeting  projections  or  irregularities  on  the  work 
operated  upon. 

The  annealing  of  high-speed  steel  should  be  done  preferably 
in  muffle  furnaces  designed  for  heating  by  radiation  only,  a 
temperature  of  1500  degrees  F.  being  maintained  for  from  twelve 
to  eighteen  hours,  according  to  the  size  and  shape  of  the  bars. 
A  series  of  experiments  made  to  determine  the  proper  temperature 
to  which  to  heat  high-speed  steel  for  annealing  gave  the  following 
results:  When  the  steel  was  heated  to  below  1250  degrees  F. 
and  slowly  cooled,  it  retained  the  original  hardness  and  brittle- 
ness  imparted  to  the  steel  in  forging.  When  heated  to  between 
1250  and  1450  degrees  F.,  the  Brinell  test  indicated  that  the 
steel  was  soft,  but  impact  tests  proved  that  the  steel  still  retained 
its  original  brittleness;  however,  when  heated  to  between  1475 
and  1525  degrees  F.,  the  steel  became  very  soft,  it  had  a  fine- 
grained fracture,  and  all  of  the  initial  brittleness  had  entirely 
disappeared.  By  carrying  these  tests  to  1600,  1750,  and  1850 
degrees  F.,  it  was  found  that  the  steel  became  very  soft,  but  there 
was  a  gradual  increase  in  brittleness  and  in  ihe  size  of  the  grain, 
until  at  1850  degrees  F.  the  steel  became  again  as  brittle  as  unan- 
nealed  steel;  the  fracture  at  this  temperature  was  dull  and 
showed  marked  decarburization. 

Dried  air-slaked  lime  was  used  as  a  packing  medium  in  making 
these  tests,  and  the  steel  was  packed  in  tubes  sealed  air-tight 
on  both  ends.  The  decarburization  that  took  place  was  probably 
due  to  the  oxygen  in  the  air  that  had  filled  the  intervening  spaces 
between  the  particles  of  lime.  This  decarburization  would  not 
have  taken  place  if  powdered  charcoal  had  been  used;  the  latter 
would  have  supplied  all  the  carbon  necessary  to  combine  with 
any  oxygen  present  in  the  tubes. 

Annealing  Methods.  —  A  method  recommended  by  one  of  the 
largest  American  high-speed  tool  steel  manufacturers  is  to  use 
an  iron  box  or  pipe  of  sufficient  size  to  allow  at  least  one-half 


HIGH-SPEED   STEEL  2-93 

inch  of  packing  between  the  pieces  of  steel  to  be  annealed  and 
the  sides  of  the  box  or  pipe.  (It  is  not  necessary  that  each  piece 
of  steel  to  be  annealed  be  kept  separate  froin  every  other  piece, 
but  only  that  the  steel  be  prevented  from  touching  the  sides  of 
the  annealing  pipe  or  box.)  This  pipe  is  packed  .carefully  with 
powdered  charcoal,  fine  dry  lime,  or  mica,  and  is  covered  with  a 
cap,  which  should  be  air-tight;  if  it  is  not,  it  should  be  luted  on 
with  fireclay.  The  pipe  is  then  heated  slowly  to  a  full  red  heat, 
about  1475  or  I5°°  degrees  F.,  and  held  at  this  heat  for  from 
two  to  eight  hours,  depending  upon  the  size  of  the  pieces  to  be 
annealed.  (A  piece  measuring  2  by  i  by  8  inches  requires  about 
three  hours'  time.)  It  is  then  cooled  as  slowly  as  possible,  care 
being  taken  not  to  expose  it  to  the  air  until  cold;  a  good  way  is 
to  allow  the  box  or  pipe  to  remain  in  the  furnace  until  cold. 

The  method  used  by  another  manufacturer  has  the  objection 
that  the  pieces  annealed  will  scale  off  somewhat,  but  as  the 
surface  is  generally  machined  away,  this  objection  is  of  no  im- 
portance for  many  classes  of  work.  The  method  is  as  follows: 
Pack  the  tools  directly  in  the  oven,  one  on  top  of  the  other, 
entirely  filling  the  furnace  if  necessary.  Heat  the  furnace  to  a 
temperature  not  exceeding  1700  or  1750  degrees  F.,  which 
should  not  require  more  than  three  hours,  and  maintain  this 
heat  for  about  two  hours,  or  until  the  temperature  of  all  the  tools 
has  been  raised  to  that  of  the  furnace  itself.  (When  smaller 
pieces  are  to  be  annealed,  it  is  sufficient  to  maintain  the  heat 
for  about  one  hour.)  Shut  off  the  heat  and  at  the  same  time 
close  all  holes,  such  as  burner  and  draft  holes,  as  carefully  as 
possible  and  let  the  tools  cool  off  in  the  furnace.  This-  cooling 
takes  place  much  more  quickly  than  when  the  other  method  is 
employed,  because  the  tools  are  not  packed;  hence,  there  is  a 
saving  in  time  not  only  in  the  heating  but  also  in  the  cooling. 
The  greater  part  of  the  expense  of  annealing  is  thus  saved  on 
account  of  the  saving  in  fuel,  and  the  elimination  of  the  packing, 
packing  materials,  and  the  boxes. 

When  it  is  desired  to  anneal  only  a  few  small  pieces,  high- 
speed steel  can  be  " water  annealed"  by  a  method  similar  to 
that  used  for  carbon  steel.  The  temperature  to  which  the  steel 


2Q4  IRON  AND   STEEL 

is  raised,  however,  is  not  as  high  as  for  carbon  steel.  In  water 
annealing,  the  piece  to  be  annealed  is  gradually  and  uniformly 
heated  to  760  degrees  F.  It  is  then  taken  from  the  furnace  and 
plunged  into  a  bath  of  pure  water,  previously  heated  to  a  tem- 
perature of  150  degrees  F.,  where  it  is  permitted  to  cool  until 
reduced  to  the  temperature  of  the  bath.  This  steel  can  be  drilled, 
filed,  or  machined  into  any  form  with  little  difficulty.  The 
more  care  devoted  to  the  heating,  the  better  will  be  the  results. 
To  heat  rapidly  will  induce  internal  strains  and  greatly  increase 
the  risk  of  breakage  when  the  pieces  are  plunged  into  the  water 
bath. 

Heat-treatment  of  Tools  having  Fine  Edges.  —  When  high- 
speed steel  is  used  for  making  tools  having  fine  cutting  edges, 
and  especially  when  such  edges  either  cannot  be  ground  or  can 
only  be  partially  ground  after  hardening,  the  hardening  operation 
is  more  difficult  than  in  the  case  of  forged  tools  for  the  lathe, 
planer,  etc.,  because  the  high  hardening  temperature  required  is 
liable  to  injure  the  cutting  edges.  For  instance,  it  is  rather  diffi- 
cult to  harden  such  tools  as  taps,  threading  dies,  gear-cutters, 
or  other  form  milling  cutters,  twist  drills,  reamers,  etc.,  because 
any  melting  or  fusing  of  the  cutting  edges  would  be  objection- 
able and  might  spoil  the  tool,  whereas,  in  the  case  of  forged 
turning  and  planing  tools,  the  fused  end  is  readily  reshaped  by 
grinding.  Tools  which  cannot  be  fused  without  injuring  them 
have  been  heated  in  barium-chloride  baths  so  that  the  steel  could 
not  be  heated  to  a  higher  temperature  than  that  of  the  bath  it- 
self, which  is  very  close  to  the  melting  point  Barium  chloride, 
however,  has  an  injurious  or  deteriorating  effect  upon  the  sur- 
face of  the  steel,  and  it  is  considered  objectionable  by  many 
manufacturers. 

One  method  of  hardening  tools  of  the  kind  referred  to  requires 
the  use  of  a  special  muffle  furnace  which  may  be  heated  either 
by  gas  or  oil.  This  furnace  has  two  chambers  lined  with  fire- 
clay and  a  series  of  burners  at  the  rear.  The  furnace  should  be 
under  such  control  that  a  temperature  of  2200  degrees  F.  may 
be  maintained  in  the  lower  chamber  while  the  upper  one  is  at  a 
much  lower  temperature.  Holes  extending  through  cutters  or 


HIGH-SPEED   STEEL  295 

other  tools  should  preferably  be  filled  with  fireclay  before  in- 
serting them  in  the  furnace.  These  tools  are  first  placed  on  top 
of  the  furnace  until  warm;  they  are  then  inserted  in  the  upper 
chamber  for  heating  to  about  1500  degrees  F.  or  to  a  medium 
red  heat.  These  heated  tools  are  then  transferred  to  the  lower 
chamber  where  they  attain  the  heat  of  this  chamber  or  about 
2200  degrees  F.  The  work  is  then  withdrawn  and  cooled  until 
warm  enough  to  just  permit  handling,  either  by  quenching  in  oil 
or  by  revolving  in  an  air  blast.  The  work  is  next  plunged  into 
a  bath  of  tallow  having  a  temperature  of  200  degrees  F.,  which 
is  next  raised  to  about  520  degrees  F.,  after  which  the  tools  are 
withdrawn  and  plunged  into  cold  oil. 

Another  method  which  is  considered  very  satisfactory  and 
which  results  in  very  little  scaling  of  the  work  requires  first  a 
thorough  cleaning  of  the  steel  from  oil  or  grease  and  the  removal 
of  all  scale.  The  tool  while  cold  is  then  immersed  in  water  and 
rolled  in  powdered  boracic  acid,  after  which  it  is  preheated  slowly 
to  about  1200  degrees  F.,  and  then  again  rolled  in  powdered 
boric  acid.  In  this  way,  the  tool  is  covered  with  a  coating  of 
boric  acid,  in  order  to  protect  it  from  decarburization.  The 
next  step  is  to  replace  the  work  in  a  furnace  and  heat  it  quickly 
to  about  2300  degrees  F.,  and  then  quench  in  an  oil  bath.  For 
tempering,  a  temperature  of  900  degrees  F.  and  cooling  in  the 
open  air  is  recommended.  The  coating  of  boric  acid  may  be 
removed  by  immersing  the  tool,  when  perfectly  cold,  in  fresh 
cold  water.  This  method  of  heat-treatment  is  particularly 
recommended  for  twist  drills,  taps,  dies,  milling  cutters,  and 
similar  tools. 

High-speed  Steel  Cutting  Ends  on  Tools.  —  High-speed  steel 
is  much  more  expensive  than  plain  carbon  steel,  principally 
because  of  the  elements,  such  as  tungsten,  etc.,  which  are  used 
to  give  the  former  its  unusual  property  of  retaining,  at  relatively 
high  temperatures,  sufficient  hardness  for  cutting  metals.  In 
order  to  reduce  the  cost  of  certain  classes  of  metal-cutting  tools, 
such  as  are  used  for  turning,  planing,  milling,  etc.,  many  manu- 
facturers use  tools  having  an  ordinary  steel  shank  and  a  high- 
speed steel  cutting  end.  This  cutting  end  or  "bit"  may  be  a 


296  IRON  AND   STEEL 

separate  piece  which  is  inserted  in  a  tool-holder  or  it  may  be 
welded  to  the  tool  shank.  The  welded  tool  is  practically  the 
same  as  a  solid  high-speed  steel  tool,  and  as  the  cutting  end  and 
shank  are  united,  the  heat  generated  by  cutting  is  conducted  from 
the  cutting  point  the  same  as  though  the  tool  were  made  entirely 
of  high-speed  steel.  When  the  welding  is  done  electrically,  a 
flat  piece  of  high-speed  steel  may  be  spot- welded  to  a  seat  formed 
at  the  end  of  the  shank,  or  an  entire  cutting  end  of  high-speed 
steel  may  be  butt-welded  to  the  shank  or  body  made  of  low- 
grade  carbon  steel.  After  the  welding  operation,  the  tool  should 
immediately  be  placed  in  a  furnace  for  heat- treatment,  because 
stresses  are  set  up  that  will  cause  the  high-speed  steel  to  check  or 
crack  if  a  decided  drop  in  temperature  occurs  after  welding.  The 
welded  tool  should  remain  in  the  furnace  for  several  hours 
and  be  cooled  very  slowly  in  order  to  secure  thorough  annealing. 
After  annealing,  the  tools  may  be  reheated,  forged,  and  temp- 
ered, the  same  as  those  made  of  solid  stock. 

Another  method  of  welding  high-speed  steel  to  low-carbon 
steel  is  by  the  Rosner  process.  The  welding  is  done  in  a  gas 
furnace  at  a  temperature  above  2000  degrees  F.,  and  a  special 
flux  is  used.  The  hardening  of  the  tool  is  done  at  the  same  time 
that  the  weld  is  made,  and  without  the  use  of  an  air  blast. 

Uses  of  High-speed  Steel.  —  The  commercial  importance  and 
value  of  high-speed  steel  in  the  machine  building  field  are  based 
primarily  upon  its  fast  cutting  qualities  in  the  removal  of  metal. 
It  is  not  economical  to  attempt  to  make  forgings  too  close  to 
the  finished  size,  and  tools  capable  of  high  cutting  speeds  and 
heavy  deep  cuts  greatly  reduce  the  machining  cost  and  increase 
production.  While  castings  can  be  molded  close  to  a  given  form 
or  size  without  difficulty,  it  is  often  necessary  to  provide  excess 
metal  which  must  afterwards  be  removed  in  order  to  secure  clean 
solid  bearing  surfaces  free  from  sandy  spongy  spots  or  other  de- 
fects, and  high-speed  steel  is  of  great  value  for  all  work  of  this 
kind.  In  some  cases,  castings  are  made  over-size  to  allow  for 
warping,  and  considerable  excess  metal  must  be  removed  for 
this  reason.  The  modern  high-speed  steel  drills  make  it  possible 
to  drill  many  holes  from  the  solid  cheaper  than  they  could  be 


HIGH-SPEED   STEEL  297 

finished  by  first  coring  and  then  using  rose  or  other  reaming 
tools.  The  great  increases  in  drilling  speeds  as  the  result  of 
high-speed  steel  drills  have  been  the  means  of  a  wonderful  ad- 
vancement in  drilling  practice  generally,  although  it  was  neces- 
sary for  the  drilling  machine  manufacturer  to  supply  a  machine 
sufficiently  rigid  and  powerful  to  enable  the  high-speed  steel 
drill  to  operate  efficiently.  Tools  made  of  high-speed  steel  are 
not  only  invaluable  for  heavy  cutting,  but  also  for  taking  light 
cuts  at  increased  speeds.  This  kind  of  steel  is  also  extensively 
used  for  other  tools  designed  to  operate  in  holes,  such  as  multiple- 
lipped  drills  and  reamers  of  the  rose  and  finishing  types.  Milling 
cutters,  gear-cutters,  forming  tools,  and  cutting-off  saws  represent 
other  very  important  applications  of  this  modern  steel  to  cutting 
tools.  Most  milling  cutters  larger  than  about  4  inches  have 
inserted  blades  attached  in  some  way  to  a  body  made  of  cheaper 
material,  and  the  inserted  blade  construction  is  also  common  to 
the  large  cutting-off  saws. 

Many  tools  which  operate  with  a  shearing  cut,  such  as  the 
blades  of  sheet-metal  shears,  punches,  and  blanking  dies  are  now 
made  of  high-speed  steel.  Blanking  dies  are  ordinarily  formed  of 
one  solid  piece  of  steel,  if  small,  whereas  larger  sizes  have  only 
a  high-speed  steel  face  in  order  to  reduce  the  cost.  Difficulty 
wliich  has  been  experienced  with  high-speed  steel  when  it  has 
been  used  for  such  tools  as  punches,  taps,  or  small  drills  has 
frequently  been  due  to  the  fact  that  the  steel  has  not  been  prop- 
erly tempered  so  as  to  secure  the  right  combination  of  hardness 
and  toughness.  Many  of  the  dies  used  for  drawing  wire  and  for 
cold-drawing  rods  or  shafting  are  made  of  high-speed  steel  be- 
cause of  its  superior  wearing  qualities.  (Dies  for  very  small 
wire  are  made  of  diamonds,  and  chilled  cast  iron  is  used  instead 
of  high-speed  steel  for  some  cold-drawing  operations.)  High- 
speed steel  has  not  only  proved  invaluable  in  machine  shops,  but 
is  used  considerably  outside  of  the  metal-working  field,  as,  for 
example,  in  the  making  of  cutters  for  wood-working  machines, 
knives  for  paper-cutting  machines,  and  for  a  variety  of  other 
purposes. 


CHAPTER  XIII 
CAST  IRON 

CAST  iron  has  been  denned  by  the  International  Association 
for  Testing  Materials  as  iron  containing  so  much  carbon  that 
it  is  not  malleable  at  any  temperature.  Iron  containing  more 
than  2.2  per  cent  of  carbon  would  conform  to  this  definition,  but 
the  carbon  content  of  ordinary  commercial  cast  iron  usually 
varies  from  3  to  4  per  cent.  The  pig  iron  obta  ned  by  smelting 
iron  ore  in  the  blast  furnace  might  properly  be  called  cast  iron, 
but  the  latter  term  is  commonly  applied  to  the  more  refined 
product  obtained  by  remelting  pig  iron  (combined  with  a  certain 
percentage  of  scrap  metal)  in  either  a  cupola  or  air  furnace  pre- 
paratory to  pouring  it  into  suitable  molds.  There  are  three 
grades  of  cast  iron  known  as  "gray  cast  iron,"  " white  cast 
iron,"  and  " mottled  cast  iron."  The  quality  of  the  cast  iron, 
or  the  grade  to  which  it  belongs,  depends  largely  upon  the  car- 
bon content  and  the  form  of  the  carbon,  or  the  extent  to  which 
it  is  chemically  combined  with  the  iron.  Much  of  the  carbon 
in  gray  cast  iron  is  in  the  form  of  graphite.  The  thin  flakes  of 
graphitic  carbon  are  mechanically  mixed  with  the  mass  of  iron, 
which  accounts  for  the  gray  appearance  of  a  fracture.  Most  of 
the  carbon  in  white  cast  iron  is  chemically  combined  with  the 
iron  instead  of  being  in  the  graphitic  state,  although  it  contains 
a  small  amount  of  graphite.  The  mottled  cast  iron  is  a  cross 
between  gray  and  white  cast  iron  or  is  an  intermediate  grade, 
part  of  the  carbon  being  chemically  combined  with  the  iron 
and  the  rest  in  a  free  or  graphitic  state.  The  gray  cast  iron  is 
much  softer  than  the  other  grades  and  less  brittle,  and  the 
white  cast  iron  is  the  hardest  and  most  brittle.  The  strongest 
grade  is  one  that  is  intermediate  between  the  extremes  of  the 
gray  and  white  qualities.  The  hardness  of  cast  iron  varies 

298 


CAST  IRON  299 

greatly,  as  the  gray  quality  may  be  very  soft  and  the  white  cast 
iron  extremely  hard  and  brittle. 

Production  of  Iron  Castings.  —  The  formation  of  iron  cast- 
ings requires,  in  the  first  place,  the  melting  of  pig  iron  and  scrap 
material  proportioned  to  produce  the  desired  quality  of  cast  iron, 
and,  in  the  second  place,  the  preparation  of  one  or  more  molds 
which  conform  to  whatever  size  and  shape  of  casting  is  to  be 
made.  That  part  of  the  work  which  includes  melting  and 
pouring  the  iron  is  known  as  "founding"  or  foundry  practice, 
whereas  the  preparation  of  the  mold  includes  patternmaking 
and  molding.  The  pattern  is  usually  made  of  wood,  although 
metal  patterns  are  common,  especially  for  making  compara- 
tively small  castings.  The  shape  of  the  pattern  conforms  to 
whatever  exterior  shape  is  required  for  the  casting,  and  interior 
openings  or  passageways  are  obtained  by  means  of  cores  set 
into  the  cavity  formed  in  the  mold  by  the  pattern.  The  mold  is 
made  of  sand  which  may  be  left  in  a  " green"  or  moist  state,  or 
the  sand  mold  may  be  baked  to  harden  it  and  make  it  more 
durable. 

The  pig  iron  and  scrap  material  are  usually  melted  in  a  fur- 
nace known  as  a  " cupola"  in  which  iron  and  fuel  are  charged 
together,  although  the  reverberatory  or  air  furnace  is  some- 
times used.  This  type  of  furnace  is  so  arranged  that  the  iron 
and  fuel  are  placed  in  separate  compartments.  When  a  cupola 
is  to  be  fired  or  prepared  for  melting  a  charge  of  iron,  the 
bottom  is  first  covered  with  a  layer  of  sand  5  or  6  inches  thick 
and  then  the  fuel  is  inserted.  Coke  is  generally  used,  but 
anthracite  coal  is  burned  in  some  cupolas.  In  addition  to  this 
bottom  bed  of  coke,  there  are  layers  of  coke  between  the  layers 
of  pig  iron  and  scrap  which  are  to  be  melted.  One  of  the  im- 
portant points  about  charging  a  cupola  is  to  determine  how  much 
fuel  there  should  be  in  the  bottom  bed  and  also  the  amount  to 
use  between  the  layers  of  iron.  The  amount  of  iron  in  the 
different  charges  is  another  important  point,  there  being,  as 
a  rule,  from  i\  pounds  up  to  4  pounds  of  iron  for  each  pound  of 
coke  in  the  bed  for  the  first  charge  of  iron.  The  succeeding 
charges  or  layers  of  iron  are  somewhat  smaller.  The  pig  iron  is 


300  IRON   AND   STEEL 

generally  thrown  into  the  cupola  first  and  then  the  scrap  material, 
because  the  latter  melts  more  readily  than  pig  iron;  the  result 
is  that  the  pig  iron  and  scrap  melt  at  about  the  same  time, 
because  the  pig  iron  reaches  the  melting  zone  first. 

Some  flux,  such  as  limestone,  also  forms  part  of  the  cupola 
charge.  This  flux  serves  two  purposes,  as  it  forms  a  slag  by 
combining  with  the  silica  from  the  charge  and  also  provides  a 
protective  covering  for  the  bath  of  molten  metal.  After  the 
cupola  has  been  charged  as  described,  it  is  generally  allowed  to 
stand  for  about  half  an  hour  before  opening  the  air  blast.  When 
this  practice  is  followed,  the  lower  part  of  the  charge  heats  up 
considerably,  and  melting  begins  rapidly  and  continues  at  a 
uniform  rate  when  the  blast  is  applied.  The  charge  of  iron  in 
the  cupola  should  be  somewhat  greater  than  is  required  for 
filling  the  molds,  because  the  iron  which  comes  out  of  the  cupola 
last  contains  more  or  less  slag  which  would  cause  defective  cast- 
ings. This  part  of  the  charge  is  commonly  used  for  making 
rough  castings  that  do  not  require  finished  surfaces.  Castings 
are  sometimes  made  from  molten  metal  obtained  directly  from 
the  blast  furnace. 

Mixtures  for  Different  Grades  of  Cast  Iron.  —  The  grade  or 
quality  of  cast  iron  depends  not  only  upon  the  proportion  of  pig 
iron  and  scrap  iron,  but  also  upon  the  grades  of  these  materials, 
as  well  as  the  flux  and  fuel  used.  There  are  many  different 
grades  and  brands  of  pig  iron,  and  the  scrap  iron  also  varies 
greatly  and  may  consist  of  cast  iron  or  steel  chips  from  machine 
shops,  the  gates  or  sprues  of  castings,  defective  castings,  wrought 
iron  scrap,  steel  scrap,  or  malleable  scrap.  A  cupola  charge 
contains  ordinarily  about  60  per  cent  of  pig  iron  and  40  per  cent 
of  scrap  when  the  castings  are  intended  for  general  work,  al- 
though for  some  special  purposes  pig  iron  alone  may  be  used. 
The  use  of  scrap  reduces  the  cost  of  the  charge,  but  increases  the 
melting  loss.  The  addition  of  steel  scrap  strengthens  the  cast- 
ings, about  25  per  cent  being  used  for  obtaining  very  strong 
castings. 

When  determining  a  cupola  mixture,  the  changes  that  occur 
while  melting  must  be  considered.  For  instance,  silicon  is 


CAST  IRON  301 

reduced  from  0.20  to  0.25  per  cent,  whereas  there  is  a  slight  in- 
crease in  the  sulphur  content.  If  the  limit  for  silicon  is  2.15  per 
cent  in  the  castings,  a  silicon  content  of  2.40  per  cent  in  the 
charge  would  be  needed  to  offset  the  0.25  per  cent  loss  in  melting. 
The  amount  of  silicon,  manganese,  and  graphitic  carbon  is 
decreased  by  remelting  iron  in  a  cupola  and  the  combined  car- 
bon is  increased.  If  soft  gray  iron  is  remelted  a  few  times, 
it  gradually  becomes  harder  and  finally  a  very  hard  white  iron  is 
produced. 

Composition  of  Cast  Iron.  —  Commercial  cast  iron  varies  con- 
siderably in  its  composition  which  depends  upon  its  intended  use. 
A  cast  iron  recommended  by  the  Society  of  Automotive  Engi- 
neers for  automobile  construction,  but  one  that  is  applicable  to 
many  other  classes  of  work,  has  the  following  composition: 
Total  carbon,  from  3.25  to  3.50  per  cent;  manganese,  preferably 
0.50  per  cent,  and  ranging  from  0.40  to  0.70  per  cent;  silicon, 
preferably  2  per  cent,  and  ranging  from  1.90  to  2.20  per  cent; 
phosphorus,  from  0.6  to  i  per  cent;  sulphur,  not  over  o.i  per 
cent.  Cast  iron  of  this  composition  is  strong  and  fairly  close- 
grained,  and  it  conforms  closely  to  the  cast  iron  used  .by  many 
machine  tool  manufacturers. 

A  committee  of  the  American  Society  for  Testing  Materials 
recommended  a  maximum  sulphur  content  in  "light"  gray 
iron  castings  of  0.08  per  cent;  in  "medium"  castings,  o.io  per 
cent;  in  "heavy"  castings,  0.12  per  cent.  These  percentages  are 
the  maximum  allowable  in  each  case.  The  term  "light  casting" 
is  applied  when  there  is  no  section  over  J  inch  thick,  and  "heavy 
casting"  is  used  when  there  is  no  section  less  than  2  inches 
thick.  The  silicon  content  should  preferably  be  varied  in  ac- 
cordance with  the  thickness  of  the  castings.  The  composition 
recommended  for  heavy  machinery  castings  is  as  follows:  Sili- 
con, from  i  to  1.5  per  cent;  sulphur,  less  than  o.io  per  cent; 
phosphorus,  from  0.30  to  0.50  per  cent;  manganese,  from  0.80 
to  i  per  cent;  total  carbon,  low.  For  medium  castings :  Silicon, 
from  1.5  to  2  per  cent;  sulphur,  less  than  0.09  per  cent;  phos- 
phorus, from  0.40  to  0.60  per  cent;  manganese,  from  0.60  to 
0.80  per  cent.  For  light  castings:  Silicon,  from  2  to  2.5  per 


302  IRON  AND   STEEL 

cent;   sulphur,  less  than  0.08  per  cent;   phosphorus,  from  0.5  to 
0.7  per  cent;   manganese,  from  0.5  to  0.7  per  cent. 

Influence  of  Carbon  on  Cast  Iron.  —  The  characteristics  of 
cast  iron  depend  chiefly  upon  the  amount  and  condition  of  the 
carbon  content.  The  influence  of  carbon,  however,  is  modified 
to  some  extent  by  other  elements  which  will  be  referred  to  later. 
The  graphite  in  gray  cast  iron,  which  is  practically  pure  carbon, 
does  not  exert  any  direct  influence  upon  the  molecules  of  the  iron, 
as  it  is  a  mechanical  mixture  and  not  chemically  combined  with 
the  iron.  Graphite  does,  however,  affect  the  tensile  strength, 
because  the  flakes  of  graphite  separate  the  grains  of  metal  and 
reduce  the  cohesion.  While  cast  iron  that  has  considerable 
graphite  is  soft  and  can  be  machined  readily,  it  has  a  relatively 
low  tensile  strength.  The  principal  factor  affecting  the  hardness, 
soundness,  tenacity,  and  freedom  from  internal  stresses  in  cast- 
ings is  the  amount  of  carbon  in  chemical  combination.  The 
amount  of  combined  carbon  varies  from  0.05  per  cent  in  the 
softest  cast  iron  to  about  0.60  per  cent  in  the  strongest  cast  iron. 
The  amount  of  silicon  and  sulphur  regulates  the  separation  of 
carbon  in  the  graphitic  form  so  that  the  sulphur  content  in- 
dicates the  relation  between  the  free  and  combined  carbon. 

Influence  of  Silicon  on  Cast  Iron.  —  Silicon  has  a  very  decided 
effect  upon  the  characteristics  of  cast  iron.  The  addition  of 
silicon  makes  the  iron  softer,  because  it  tends  to  separate  the 
carbon  as  graphite  and  the  hardening  effect  of  the  silicon  re- 
quired to  do  this  is  less  than  that  of  the  combined  carbon  con- 
verted into  free  or  graphitic  carbon.  By  varying  the  silicon 
content,  the  quality  of  the  cast  iron  can  be  changed  according 
to  its  intended  use,  although  the  effect  of  other  elements  must 
not  be  ignored.  A  silicon  content  of  1.8  per  cent  gives  the 
maximum  tensile  strength  and  a  silicon  content  of  0.9  per  cent 
gives  the  maximum  crushing  strength.  The  greatest  general 
strength,  including  crushing,  tensile,  and  transverse  is  obtained 
with  a  silicon  content  of  1.4  per  cent. 

Influence  of  Sulphur,  Manganese,  and  Phosphorus.  —  The1 
addition  of  sulphur  increases  the  hardness  and  brittleness  of 
cast  iron,  its  effect  being  opposite  to  that  of  silicon.  Sulphur 


CAST  IRON  303 

also  tends  to  cause  defective  castings  as  it  makes  the  iron  more 
sluggish  when  pouring  it  into  the  mold.  Sulphur  also  increases 
the  shrinkage  and  resulting  internal  stresses.  For  these  reasons 
it  is  essential  to  keep  the  sulphur  content  low,  particularly  if  the 
castings  are  small. 

The  effect  of  manganese  is  also  opposite  to  that  of  silicon  as  it 
retards  the  separation  of  graphite  by  combining  with  the  car- 
bon, thus  making  the  iron  harder  and  stronger.  Manganese 
also  combines  with  sulphur  and  is  removed  with  the  slag. 

Phosphorus  increases  the  hardness  and  brittleness  of  castings 
and  reduces  the  tensile  strength,  but  it  lowers  the  melting  point 
and  increases  the  fluidity  of  the  molten  iron. 

Other  Alloying  Elements  for  Cast  Iron.  —  Chromium,  nickel, 
titanium,  and  vanadium  have  been  introduced  into  cast  iron, 
although  they  are  less  common  than  the  other  elements  previ- 
ously referred  to.  Chromium  strengthens  cast  iron,  but  makes 
it  hard  and  brittle.  The  use  of  i  or  2  per  cent  of  nickel 
strengthens  cast  iron  and  improves  its  chilling  power,  but  it  is 
not  used  to  any  great  extent  on  account  of  the  cost.  Heavy 
chilled  castings  such  as  car  wheels  and  rolling  mill  rolls  some- 
times contain  nickel  or  chromium.  It  is  doubtful  if  titanium  is 
beneficial  in  cast  iron,  for  while  it  tends  to  remove  the  sulphur, 
this  is  offset  by  the  removal  of  oxygen  which  is  highly  beneficial. 
In  fact,  titanium  is  one  of  the  best  deoxidizers  known  in  metal- 
lurgy. The  influence  of  vanadium  is  to  increase  the  resistance 
of  the  cast  iron  to  wear. 

Strength  of  Cast  Iron.  —  The  ultimate  tensile  strength  of 
cast  iron  may  generally  be  assumed  to  be  15,000  pounds  per 
square  inch;  the  ultimate  shearing  strength,  18,000  pounds  per 
square  inch;  the  ultimate  compressive  strength,  80,000  pounds 
per  square  inch;  and  the  modulus  of  elasticity,  12,000,000. 
Castings  are  usually  under  considerable  internal  strain  as  the 
result  of  unequal  contraction,  although  this  strain  may  gradu- 
ally disappear.  The  working  stresses  for  ordinary  castings 
should  be  limited  to  from  2000  to  4000  pounds  per  square  inch, 
depending  upon  the  service.  If  loads  are  to  be  applied  suddenly, 
the  tensile  strength  should  be  limited  to  2000  pounds  per  square 


304  IRON  AND   STEEL 

inch  and  if  the  direction  of  the  load  reverses,  the  limit  should 
be  1000  pounds  per  square  inch.  It  may  be  necessary  to  further 
limit  these  unit  loads  to  suit  the  ratio  of  the  length  to  the  sec- 
tion, as  required  for  columns  or  other  parts  in  alternate  ex- 
tension and  compression.  The  strength  of  cast  iron  begins  to 
decrease  when  the  temperature  rises  above  approximately  500 
degrees  F.;  at  900  degrees  F.,  it  has  75  per  cent  of  the  original 
strength;  and  at  noo  degrees  F.,  40  per  cent  of  the  original 
strength.  The  melting  point  of  cast  iron  is  about  2300  degrees 
F.,  and  its  specific  gravity,  about  7.2,  the  weight  per  cubic  inch 
being  0.26  pound. 

Growth  of  Castings  or  Change  in  Size.  —  Cast-iron  parts 
which  are  subjected  to  repeated  heating  and  cooling  gradually 
increase  in  size  or  "grow,"  which  is  a  quality  peculiar  to  cast 
iron.  This  growth  is  so  pronounced  that  annealing  ovens  8 
feet  in  length  have  been  known  to  grow  to  9  feet  in  length  as 
the  result  of  being  heated  red  hot  for  prolonged  periods  between 
which  they  are  permitted  to  cool.  Furnace  grates  and  similar 
parts  are  affected  in  the  same  way.  Experiments  have  shown 
that  the  maximum  growth  of  commercial  cast  iron  occurs  when 
it  is  heated  to  a  temperature  of  1650  degrees  F.  during  four-hour 
periods,  between  which  the  casting  is  cooled.  Cast  iron  sub- 
jected to  this  treatment  increased  in  size  from  35  to  37 J  per 
cent,  and  the  weight  increased  from  7.8  to  8.6  per  cent.  This 
increase  of  weight  indicates  that  gases  were  absorbed  from  the 
air,  there  being  an  oxidation  of  silicon  and  of  carbon.  The 
effect  of  gases  on  the  growth  of  cast  iron  was  shown  by  the  fact 
that  a  test  piece  increased  in  size  and  weight  decidedly  when 
heated  in  a  mufHe  furnace,  but  contracted  slightly  when  heated 
in  a  vacuum.  White  cast  iron  is  preferable  to  the  gray  cast 
iron  where  difficulty  is  experienced  on  account  of  growth.  It 
should  contain  about  3  per  cent  of  carbon  and  the  silicon  con- 
tent should  not  exceed  from  0.2  to  0.3  per  cent. 

Methods  of  Hardening  Castings.  —  Either  rough  castings  or 
those  which  have  been  machined  can  be  hardened  throughout 
by  subjecting  them  to  the  following  heat- treatment :  After 
heating  the  casting  to  a  cherry-red,  it  is  quenched  in  a  bath, 


CAST  IRON  305 

preferably  of  sulphuric  acid  (having  a  specific  gravity  of  from 
1.8  to  1.85)  to  which  is  added  a  suitable  quantity  of  arsenic. 
Three-fourths  pound  of  red  arsenic  crystals  to  one  gallon  of 
sulphuric  acid  having  a  specific  gravity  of  about  1.84  is  preferable. 
To  obtain  the  best  results,  the  red  arsenic  crystals  should  be 
added  to  the  sulphuric  acid  and  the  bath  should  not  be  used  for 
about  a  week,  to  insure  thorough  saturation.  This  bath  has  a 
high  heat-conducting  power  which  is  essential,  and  the  more 
rapidly  the  cast  iron  is  cooled,  the  harder  it  is  made.  The 
bath  should  be  contained  in  a  lead  jar  or  tank  surrounded  by  a 
water  jacket.  If  only  one  section  of  a  casting  requires  hardening, 
this  may  be  done  by  simply  immersing  that  part. 

Seasoning  Cast  Iron.  —  Cast  iron,  like  steel,  is  subject  to  more 
or  less  change  of  shape,  particularly  after  the  hard  outer  skin 
or  surface  has  been  removed  by  turning  or  planing.  One  method 
of  avoiding  these  changes  in  the  finished  part  is  to  allow  the 
castings  to  "season"  or  stand  for  several  weeks  or  even  months 
after  taking  the  roughing  cuts  and  before  finishing  them.  These 
changes  are  caused  by  the  internal  stresses  in  the  casting,  which 
are  gradually  readjusted  and  neutralized  by  seasoning. 

In  order  to  avoid  a  long  seasoning  period,  castings  that  must 
retain  their  shape  as  much  as  possible  are  often  subjected  to 
some  kind  of  heat- treatment.  A  method  which  has  proved 
successful,  as  applied  to  the  cast-iron  beds  of  measuring  machines, 
is  in  the  nature  of  an  annealing  process.  After  rough-machining, 
castings  are  placed  in  a  furnace  and  heated  to  a  low  red  heat. 
Another  method  of  annealing  is  by  dipping  the  casting  repeatedly 
in  hot  water.  The  release  of  the  internal  stresses  will  also  be 
accelerated  if  the  casting  is  subjected  to  repeated  shocks  or 
vibration,  while  cold.  In  making  surface  plates  and  straight- 
edges, good  results  have  been  obtained  by  first  rough-planing 
the  work  and  then  subjecting  it  to  a  temperature  varying  be- 
tween 350  and  550  degrees  F.,  the  temperature  depending  upon 
the  size  and  shape  of  the  casting.  After  this  heat-treatment, 
the  castings  are  finish-machined  and  then  scraped.  Even  though 
a  casting  is  well-seasoned,  the  shape  may  change  if  it  is  subjected 
to  unusual  degrees  of  heat  and  cold,  but  unless  these  changes  are 


306  IRON  AND   STEEL 

sufficient  to  cause  warping,  the  casting  will  return  to  its  original 
shape.  Castings  that  have  been  left  in  the  yard  and  exposed  to 
the  weather  for  a  long  period  will  be  seasoned  the  same  as  those 
which  have  been  heat-treated. 

Chilled  Castings.  —  The  hardness  of  cast  iron  depends  en- 
tirely upon  the  condition  of  the  carbon  it  contains.  If  the  iron 
is  cooled  so  rapidly  that  the  crystals  or  flakes  of  graphite  will 
not  have  time  to  separate,  the  carbon  will  remain  in  the  combined 
form  and  a  very  hard  iron  will  be  produced.  In  the  production 
of  chilled  castings,  this  rapid  cooling  is  effected  either  by  metallic 
molds  or  by  inserting  pieces  of  iron  or  " chills"  into  the  mold. 
When  the  molten  metal  comes  into  contact  with  these  metallic 
surfaces,  it  is  cooled  rapidly  and  thus  hardened.  The  more 
rapid  the  rate  of  cooling,  the  whiter  will  be  the  iron  and  the 
greater  the  depth  of  the  chilled  or  hardened  part.  These  hard 
outer  surfaces  on  chilled  castings  are  desirable  for  many  purposes, 
especially  where  the  surface  of  the  casting  is  subjected  to  con- 
siderable abrasion  or  wear.  Steel  castings  are  used  for  the  jaws 
of  crushing  machines,  stamps,  certain  classes  of  rolls,  and  for 
many  other  purposes.  The  wearing  surfaces  of  machine  tool 
beds  are  often  chilled  to  produce  a  better  wearing  surface  by  in- 
creasing the  density  and  hardness  of  the  metal. 

The  depth  of  the  chilled  part  of  a  casting  may  vary  from  J 
to  i  inch  or  more,  and  it  is  partly  dependent  upon  the  thickness 
of  the  chill  or  the  metallic  part  of  the  mold,  and  to  some  extent 
upon  the  temperature  of  the  metal  when  poured.  While  the  outer 
surface  of  a  chilled  casting  is  extremely  hard,  the  inner  surface 
is  comparatively  soft  and  tough.  The  chilling  process,  or  the  use 
of  chills  in  molds,  is  not  only  employed  to  secure  hard  castings, 
but  also  to  obtain  a  more  uniform  cooling  of  the  metal;  in  fact, 
chills  are  sometimes  used  primarily  to  control  the  rate  of  cooling. 
When  a  casting  has  a  heavy  section  adjoining  a  relatively  light 
section,  the  latter  naturally  tends  to  cool  more  rapidly,  which 
may  result  in  a  defective  casting,  on  account  of  the  metal  being 
drawn  away  from  the  thick  section  at  the  point  where  it  joins  the 
thinner  part.  This  may  be  avoided  and  the  formation  of  in- 
ternal cavities  prevented  by  using  chills  which  will  cause  the 


CAST  IRON  307 

heavy  section  to  cool  more  rapidly.  If  the  section  that  is 
chilled  in  this  way  must  be  machined  afterwards,  care  must 
be  taken  to  use  chills  that  are  just  thick  enough  to  increase  the 
rate  of  cooling  the  required  amount.  If  the  chills  are  too  thick, 
the  casting  will  be  hardened  excessively  and  machining  will  be 
either  difficult  or  impossible. 

The  car  wheel  is  one  of  the  most  common  as  well  as  impor- 
tant examples  of  chilled  castings.  The  tread  or  periphery  of 
such  wheels  is  chilled  so  that  they  will  resist  wear,  due  to  rolling 
on  the  rails  and  the  abrasive  action  of  the  brakes.  The  chilled 
section  usually  extends  to  a  depth  of  from  f  to  f  inch.  This 
hard  outer  surface  gradually  changes  into  the  ordinary  gray  cast 
iron  of  which  the  remainder  of  the  wheel  is  composed.  The 
iron  used  for  making  car  wheels  is  selected  by  chemical  analysis. 
The  controlling  element  in  the  formation  of  the  chilled  surface  is 
silicon.  If  the  silicon  content  is  higher  than  0.80  or  0.90  per 
cent,  the  chilling  effect  will  not  be  obtained,  and  for  this  reason 
iron  of  low  silicon  content  must  be  used.  The  use  of  the  right 
grade  of  coke  for  melting  the  iron  is  also  very  essential,  what  is 
known  as  the  " 7 2-hour  coke"  being  commonly  used.  The 
chill  in  the  mold  is  in  the  form  of  a  ring  which  surrounds  the 
wheel  tread.  This  chill  may  be  a  plain  smooth  ring,  or  it  may 
be  arranged  to  contract  as  the  mold  cools.  When  a  plain  ring  is 
used,  it  naturally  expands  when  heated  and  moves  away  from 
the  shrinking  metal  of  the  wheel.  To  avoid  this,  the  "  con- 
tracting chill"  has  been  used.  A  simple  form  consists  of  a  ring 
having  a  large  number  of  radial  slots  extending  through  the 
inner  half.  When  the  molten  metal  comes  into  contact  with 
the  inner  ends  of  the  radial  sections  formed  by  the  slots,  these 
are  heated,  but  the  outer  ring  remains  comparatively  cold,  so 
that  the  expansion  of  the  radial  sections  actually  reduces  the 
inside  diameter  and  the  chill  contrac-ts  with  the  wheel.  The 
outer  ring  may  be  hollow  and  have  a  stream  of  water  circu- 
lating through  it  to  keep  it  cool.  Car  wheels  are  annealed  after 
casting  by  placing  them  in  a  pit  while  still  red,  where  they  are 
allowed  to  remain  while  they  cool  slowly. 


308  IRON   AND    STEEL 

Malleable  Iron  Castings.  —  Ordinary  castings  are  quite  brittle 
and  are  often  broken  by  a  shock  or  blow.  In  order  to  secure  a 
tougher  material,  ordinary  white-iron  castings  are  subjected  to 
a  heat-treating  or  annealing  process  which  makes  them  partly 
malleable  and  much  tougher  than  unannealed  castings.  The 
castings  that  are  to  be  made  malleable  are  produced  in  the  or- 
dinary manner  except  that  an  air  furnace  is  generally  used. 

The  softest  and  most  ductile  constituent  in  any  iron  product  is 
ferrite,  which  is  observed  in  carbonless  iron  when  a  polished  and 
etched  specimen  is  examined  under  the  microscope.  As  a  good 
grade  of  wrought  iron  is  very  low  in  carbon,  it  consists  princi- 
pally of  ferrite,  although  there  are  minute  particles  of  slag  which 
cannot  be  entirely  removed  in  the  process  of  manufacture.  The 
object  of  annealing  white-iron  castings  is  to  separate  the  hard 
carbide  of  iron  into  iron  and  carbon;  consequently  the  outer 
part  of  the  casting  is  changed  to  ferrite  and  the  interior  is  made 
up  of  ferrite  contaminated  with  free  carbon.  The  structural 
composition  of  wrought  iron  and  malleable  iron  is  similar,  with 
the  exception  of  the  slag  in  wrought  iron  and  the  free  carbo'h  in 
malleable  iron. 

While  malleable  cast  iron  is  not  as  strong  as  steel  and  is  not 
suitable  when  a  high  tensile  strength  is  required,  it  will  with- 
stand shocks  better  than  ordinary  steel  and  can  be  bent  or 
twisted.  One  of  the  great  advantages  of  malleable  iron  is  that 
it  is  not  subject  to  crystallization  or  " fatigue"  and  it  is  capable 
of  resisting  repeated  shocks  for  long  periods.  In  fact,  it  is 
claimed  that  a  good  grade  of  malleable  iron  will  stand  as  severe 
a  test  after  twenty-five  years  of  use  as  when  originally  made. 
Malleable  iron  also  resists  corrosion  much  better  than  either 
steel  or  wrought  iron.  The  tensile  strength  of  malleable  cast- 
ings ordinarily  varies  from  35,000  to  55,000  pounds  per  square 
inch,  with  from  3  to  8  per  cent  elongation  in  two  inches. 

When  making  castings  that  are  to  be  converted  into  the  mal- 
leable product,  it  is  essential  to  use  the  proper  grade  of  pig 
iron,  to  pour  the  metal  rapidly,  to  secure  sufficient  oxidation 
of  the  silicon  and  carbon,  and  finally  to  anneal  the  castings 
properly.  An  air  furnace  is  generally  used  for  melting  the  charge 


CAST  IRON  309 

for  castings  that  are  afterwards  to  be  made  malleable.  The 
open-hearth  furnace  has  also  been  used  to  some  extent.  While 
a  cupola  may  be  used,  the  metal  is  liable  to  burn  and  more  diffi- 
culty is  experienced  with  defective  castings;  consequently,  the 
use  of  the  cupola  for  this  branch  of  foundry  work  is  practically 
obsolete.  A  higher  annealing  temperature  is  also  required  than 
is  necessary  when  the  air  or  open-hearth  furnace  is  used.  The 
melting  cost,  however,  is  lower  when  using  a  cupola. 

Prior  to  annealing  the  castings,  they  are  cleaned  either  by 
tumbling,  pickling,  or  by  means  of  a  sand-blast.  They  are  then 
placed  in  malleable-iron  annealing  boxes  or  pots  and  the  spaces 
between  the  castings  are  filled  with  crushed  slag,  rolling  mill 
scale,  or  a  mixture  of  both.  Hematite  ore  is  also  used,  especially 
if  a  cupola  was  used  when  making  the  castings.  The  minimum 
temperature  in  the  annealing  furnace  should  be  1350  degrees 
F.  and  the  maximum,  1450  degrees  F.  The  furnace  is  quickly 
heated  to  the  desired  temperature,  which  is  maintained  for  about 
sixty  hours.  The  furnace  is  then  cooled  slowly  until  the  pots 
are  black,  and  then  the  contents  are  removed.  Natural  gas  is 
considered  the  best  fuel  for  annealing  furnaces,  although  pro- 
ducer gas  is  satisfactory.  Some  castings  are  annealed  without 
packing  them  in  annealing  pots  as  described.  In  this  case,  a 
muffle  oven  is  used.  The  castings  are  packed  in  the  oven  with 
the  scale  or  other  material.  This  method  is  applied  when  the 
castings  are  long  or  of  such  a  shape  that  pots  cannot  readily  be 
used. 

The  composition  of  a  malleable  iron  recommended  by  the 
Society  of  Automotive  Engineers  is  as  follows:  Manganese, 
preferably  0.50  per  cent,  but  varying  from  0.30  to  0.70  per  cent; 
silicon,  i  per  cent  maximum  and  0.60  per  cent  desired;  phos- 
phorus, 0.20  per  cent  maximum  and  0.17  per  cent  desired;  sul- 
phur, 0.06  per  cent  maximum.  A  malleable  casting  which 
varies  decidedly  from  the  composition  given  is  liable  to  be 
brittle,  and  in  any  case  proper  annealing  is  necessary.  Malle- 
able castings  are  extensively  used  in  the  manufacture  of  agri- 
cultural machinery,  and  also  in  railway  equipment  and  for 
many  other  classes  of  work  subjected  to  shocks  and  corrosion. 


CHAPTER  XIV 
STEEL   CASTINGS 

STEEL  castings  are  formed  by  pouring  molten  steel  into  suit- 
able molds,  the  general  procedure  in  this  respect  being  prac- 
tically the  same  as  in  the  iron  foundry.  The  shape  of  a  steel 
casting,  like  one  made  of  cast  iron,  depends  entirely  upon  the 
shape  of  the  mold,  and  it  is  not  rolled  or  forged.  The  steel  used 
for  making  steel  castings  may  be  produced  either  by  the  Bessemer, 
open-hearth,  electric,  or  crucible  processes.  The  steel  cannot  be 
melted  in  a  cupola,  because  the  impurities  will  be  absorbed  from 
the  fuel,  and  it  is  also  difficult  to  obtain  the  high  temperature 
necessary.  The  terms  "cast  steel"  and  " steel  casting"  are 
sometimes  used  interchangeably.  Tool  or  crucible  steel  was 
formerly  known  as  cast  steel,  but  this  usage  of  the  term  "cast 
steel"  is  now  almost  obsolete  and  should  be  discontinued,  be- 
cause it  results  in  confusion  as  to  the  intended  meaning. 

Steel  castings  are  especially  useful  for  machine  parts  that  must 
withstand  thrust  or  shocks  or  those  subjected  to  heavy  loads. 
Great  improvements  have  been  made  in  the  production  of  steel 
castings,  especially  in  regard  to  the  tensile  strength,  elastic  limit, 
and  resistance  to  impact.  Steel  castings  are  stronger  than  either 
wrought  iron,  cast  iron,  or  malleable  iron,  and  they  are  very 
tough.  Steel  castings  are  used  for  such  parts  as  cylinder  covers, 
cross-heads,  cross-head  guides,  valve  chest  covers,  bearing  caps, 
bed-plates  and  housings,  sternposts  for  ships,  rudder  frames, 
gun  mounts,  locomotive  side  frames,  etc.  Steel  castings  are  of 
special  importance  in  ship  construction  and  for  various  classes 
of  railway  equipment,  although  they  are  applied  in  a  great 
variety  of  industries. 

Strength  of  Steel  Castings.  —  The  tensile  strength  of  steel 
castings  has  been  increased  about  50  per  cent  during  a  period  of 
twenty-five  years,  and  the  resistance  to  impact  has  been  increased 

310 


STEEL  CASTINGS  311 

to  a  still  greater  extent.  The  tensile  strength  of  steel  castings 
produced  in  modem  steel  foundries  ordinarily  varies  from  60,000 
to  80,000  or  85,000  pounds  per  square  inch.  The  specifications 
prescribed  by  the  American  Society  for  Testing  Materials  in- 
clude two  general  classes  of  steel  castings  known  respectively  as 
Class  A  and  Class  B.  The  former  represents  ordinary  castings 
for  which  no  physical  requirements  are  specified.  The  Class  B 
castings  for  which  physical  requirements  are  specified  are  divided 
into  three  grades,  designated  as  hard,  medium,  and  soft.  The 
minimum  requirements  as  to  tensile  properties  for  Class  B  cast- 
ings are  as  follows:  Soft  grade,  tensile  strength,  60,000  pounds 
per  square  inch;  yield-point,  27,000  pounds  per  square  inch; 
elongation  in  two  inches,  22  per  cent;  reduction  of  area,  30 
per  cent.  For  the  medium  grade,  tensile  strength,  70,000 
pounds  per  square  inch;  yield-point,  31,500  pounds  per  square 
inch;  elongation  in  two  inches,  18  per  cent;  reduction  of  area, 
25  per  cent.  For  the  hard  grade,  tensile  strength,  80,000  pounds 
per  square  inch;  yield-point,  36,000  pounds  per  square  inch; 
elongation  in  two  inches,  15  per  cent;  reduction  of  area,  20  per 
cent. 

The  specifications  of  the  Ordnance  Department  require  mini- 
mum tensile  strengths  varying  from  60,000  to  85,000  pounds 
per  square  inch  for  different  grades  of  castings,  with  yield- 
points  varying  from  28,000  to  53,000  pounds  per  square  inch; 
reduction  of  area,  from  20  to  30  per  cent;  and  elongation  in 
two  inches,  from  17  to  22  per  cent.  Test-bars  J  by  i  inch  must 
withstand  being  bent  cold  through  an  angle  of  120  degrees 
around  a  i-inch  pin.  As  steel  castings  are  much  stronger  and 
tougher  than  cast-iron  castings,  they  can  be  made  thinner  and 
lighter,  which  is  an  important  feature  for  many  classes  of  serv- 
ice. 

Materials  for  Making  Steel  Castings.  —  The  raw  materials 
from  which  steel  castings  are  made  are  steel  scrap,  pig  iron,  and 
iron  ore,  the  materials  and  their  proportions  varying  according 
to  the  process  and  the  type  of  furnace  used.  The  scrap  is  made 
up  of  the  cropped  ends  of  plates,  forgings,  and  structural  material, 
and  the  borings  and  turnings  from  machine  shops.  The  amount 


312  IRON  AND    STEEL 

of  ore  required  depends  upon  the  nature  of  the  other  ingredients. 
In -some  cases,  where  scrap  could  not  be  procured,  the  charge  has 
consisted  entirely  of  pig  iron  and  ore.  The  ore  is  used  chiefly 
for  its  oxidizing  effect  on  the  metalloids,  carbon,  silicon,  sulphur, 
and  phosphorus.  Hematite  ore  is  the  kind  generally  used,  and 
the  iron  it  contains  is  a  secondary  consideration. 

Processes  for  Making  Steel  Castings.  —  The  method  of  mak- 
ing steel  castings  varies  according  to  the  process  of  melting  the 
raw  materials  or  of  producing  the  steel,  and  in  regard  to  certain 
other  details  which  will  be  referred  to.  The  steel  for  compara- 
tively small  castings  may  be  made  by  the  Bessemer  or  crucible 
processes,  whereas  for  large  castings  the  open-hearth  furnace  is 
preferable.  The  electric  furnace  is  now  used  extensively  in 
connection  with  this  work,  as  explained  later.  The  crucible 
process  is  sometimes  used  for  making  very  thin  castings,  as  the 
metal  may  be  poured  directly  from  the  crucible  which  is  kept  in 
the  furnace  until  needed.  Ladles  may  also  be  used,  especially 
for  the  larger  castings.  The  crucible  process  is  adapted  to  cast- 
ings made  of  ordinary  carbon  steel  (except  when  the  carbon  con- 
tent is  very  low)  and  of  nickel-chromium,  tungsten,  or  molyb- 
denum steels.  Manganese  steel  can  be  produced  more  profit- 
ably by  the  Bessemer  process. 

In  most  American  steel  foundries  using  Bessemer  converters, 
the  side-blown  type  is  employed.  These  converters  all  have 
an  acid  lining  because  of  the  melting  losses  incident  to  the 
Bessemer  process.  The  basic  converter  is  used  in  some  parts  of 
Europe.  The  air  or  blast  of  these  side-blown  converters  passes 
through  a  trunnion  and  then  through  tuyeres  at  the  side.  When 
an  ordinary  converter  is  used,  a  cupola  is  required  for  melting 
the  charge  and  a  smaller  cupola  for  melting  the  recarburizers 
and  alloys.  When  a  converter  is  to  be  blown,  it  is  preheated 
either  by  placing  a  fire  in  it  or  by  means  of  an  oil  burner.  This 
preheating  continues  for  three  or  four  hours,  and  when  it  is 
blown  to  a  yellow  heat,  it  is  tipped  forward  and  charged  with 
molten  metal  from  the  cupola.  The  blast,  which  has  a  pressure 
of  about  four  pounds  per  square  inch,  is  then  turned  on.  After 
the  charge  has  boiled  four  or  five  minutes  at  intervals  of  from 


STEEL   CASTINGS  313 

3  to  10  minutes,  the  " final  flame"  appears,  and  then  the  blast 
is  shut  off  and  the  charge  is  re-carburized  and  is  ready  for  pouring. 
In  order  to  avoid  using  a  cupola  for  melting  the  charge, 
which  makes  it  necessary  to  convey  the  molten  metal  from  the 
cupola  to  the  converter,  what  is  known  as  a  stock  converter  is 
sometimes  used.  The  pig  iron  and  scrap  are  charged  into  this 
converter,  and  when  this  charge  is  melted,  the  metal  is  blown  in 
the  usual  manner.  Oil  burners  are  used  for  melting  the  charge; 
however,  unless  oil  is  very  cheap  and  coke  is  expensive,  this 
method  is  not  profitable. 

The  open-hearth  process  is  considered  economical  when  cast- 
ings are  to  be  made  that  average  over  50  pounds  in  weight. 
The  open-hearth  furnaces  used  in  American  steel  foundries  are 
usually  of  from  15  to  20  tons  capacity,  although  they  vary  from 
8  to  about  35  tons  capacity.  Open-hearth  steel  would  be  suit- 
able for  making  small  castings  were  it  not  for  the  difficulties 
due  to  a  rather  low  initial  temperature  and  the  chilling  of  the 
metal  when  an  attempt  is  made  to  pour  a  large  number  of  small 
castings.  The  disadvantages  of  the  process  are  that  only  one 
kind  of  steel  can  be  made  in  one  heat;  the  furnace  must  be 
worked  continuously;  and  the  initial  cost  of  the  installation  is 
relatively  high. 

When  the  acid  process  is  employed,  the  charge  contains  from 
20  to  35  per  cent  of  pig  iron,  the  remainder  being  scrap.  The 
scrap  is  low  in  carbon  and  considerable  pig  iron  is  necessary  to 
make  the  steel  boil.  More  pig  iron  is  used  in  making  basic  steel, 
the  proportion  being  about  half  pig  iron  and  half  scrap.  Some 
open-hearth  furnaces  are  of  the  rolling  or  tilting  type  so  that, 
when  the  metal  is  ready  to  pour,  the  melting  chamber  is  tilted 
by  means  of  electric  or  hydraulic  machinery  until  the  metal 
flows  from  the  spout  into  the  ladle.  Another  type  of  furnace  is 
so  arranged  that  it  can  be  lifted  from  its  setting  for  pouring  the 
metal  directly  into  the  molds,  a  crane  being  used  to  convey  the 
furnace  from  one  mold  to  another. 

The  molds  for  making  steel  castings  must  be  made  of  some 
material  that  will  withstand  considerable  heat,  as  the  pouring 
temperature  for  steel  varies  between  2500  and  2700  degrees  F. 


314  IRON  AND   STEEL 

Because  of  this  high  temperature,  molding  sand  must  contain 
enough  silica  to  prevent  melting  or  softening  by  the  heat  of  the 
steel.  Sand  having  considerable  silica  is  often  mixed  with  just 
enough  fireclay  to  give  the  necessary  plasticity. 

Electric  Furnace  in  the  Steel  Foundry.  —  The  electric  furnace 
has  proved  valuable  for  making  steel  castings  as  well  as  for 
producing  special  alloy  and  tool  steels,  and  many  of  these  fur- 
naces have  been  installed  in  steel  foundries.  The  electric  fur- 
nace produces  a  very  pure  steel  and  the  high  temperatures 
obtainable  make  it  possible  to  cast  very  light  sections.  In  fact, 
the  temperature  may  be  varied  according  to  requirements,  lower 
temperatures  being  maintained  when  pouring  relatively  large 
castings.  The  use  of  the  electric  furnace  tends  to  eliminate 
blow-holes  or  pipes  in  castings,  and  any  alloying  elements  that 
may  be  required  can  be  added  in  the  furnace.  Electric  furnaces 
of  the  larger  sizes  are  sometimes  used  in  conjunction  with  open- 
hearth  furnaces  and  Bessemer  converters.  The  partially  re- 
fined molten  charge  may  be  obtained  either  from  an  open-hearth 
furnace  or  a  Bessemer  converter,  as  in  the  duplex  or  "hot  metal" 
process,  or  the  converter,  open-hearth  furnace,  and  electric  fur- 
nace may  be  used  in  combination  as  in  the  triplex  process,  which 
is  described  more  in  detail  in  Chapter  IX.  The  basic  electric 
furnace  is  generally  used  in  steel  foundries  as  well  as  in  other 
branches  of  the  steel  industry.  The  basic  slag  which  may  be 
used  with  the  basic  electric  furnace  reacts  chemically  with  the 
impurities  in  the  molten  charge  and  removes  them  the  same  as 
with  the  basic  open-hearth  furnace.  Thus  phosphorus  may  be 
removed  by  the  use  of  oxides  in  the  slag  and  also  sulphur  and 
oxygen,  since  the  electric  furnace  can  operate  under  reducing  or 
oxidizing  conditions.  If  the  specifications  as  to  the  sulphur  and 
phosphorus  contents  in  the  castings  aie  not  exacting  and  a  good 
quality  of  scrap  is  available,  an  acid-lined  furnace  may  be  used. 
The  general  practice  when  the  charge  is  melted  in  the  furnace  is 
to  melt  rapidly  and  then'  allow  the  molten  steel  to  remain  in  the 
furnace  long  enough  for  deoxidizing,  after  which  it  is  poured. 

Annealing  Steel  Castings.  —  Steel  castings  are  ordinarily  an- 
nealed by  heating  them  in  a  furnace  to  a  temperature  which  is 


STEEL  CASTINGS 


315 


usually  between  1500  and  1600  degrees  F.  This  heat-treatment, 
if  properly  conducted,  improves  the  granular  structure  of  the 
metal,  increases  its  ductility  and  tensile  strength,  and  also  re- 
lieves internal  stresses  in  the  castings.  The  annealing  furnace 
may  be  heated  by  coal,  oil,  natural  gas,  or  producer  gas.  It  is 
essential  to  secure  even  or  uniform  heating  of  the  castings,  and 
all  the  castings  in  a  charge  should  be  of  practically  the  same 
size.  If  some  castings  are  large  and  others  quite  small,  the  lat- 
ter will  be  injured  by  oxidation  in  scaling  and  the  large  sizes 


Fig.  i.    Cast-steel  Rudder  Frame  which  weighs  about  20  Tons 

may  not  be  sufficiently  annealed.  The  annealing  practice  recom- 
mended by  the  American  Society  for  Testing  Materials  is  as 
follows : 

1.  The  castings  should  preferably  be  sufficiently  cleaned  of 
adhering  sand  before  annealing,  to  insure  thorough  and  uniform 
heating. 

2.  The  castings  should  be  heated  slowly  and  uniformly  to 
temperatures  varying  with  the  carbon  content  of  the  steel,  and 
approximately  as  follows:     Carbon,  up  to  0.16  per  cent,  925 


316  IRON  AND   STEEL 

degrees  C.  (1607  degrees  F.);  from  0.16  to  0.34  per  cent  of 
carbon,  875  degrees  C.  (1609  degrees  F.);  from  0.35  to  0.54  per 
cent  of  carbon,  850  degrees  C.  (1562  degrees  F.);  from  0.55  to 
0.79  per  cent  of  carbon,  830  degrees  C.  (1526  degrees  F.). 

Nothing  in  these  recommendations  shall  be  understood  as 
preventing  the  temperatures  being  50  and,  in  special  cases,  100 
degrees  C.  higher  than  those  given  in  the  table,  when  necessary 
to  attain  the  desired  result. 

3.  The  castings  should  be  kept  at  the  maximum  temperature 
a  sufficient  length  of  time  to  insure  the  refining  of  the  grain.  In 


Fig.  2.     Cast-steel  Sternpost  for  Torpedo  Boat  Destroyer 

general,  the  heavier  the  sections  of  the  casting,  the  longer  must 
be  the  time  of  exposure  to  the  maximum  temperature. 

4.  The  castings  should  be  cooled  slowly  and  uniformly  in 
the  furnace,  when  it  is  desired  that  the  steel  shall  possess  the 
maximum  softness. 

The  castings  may  be  cooled  at  an  accelerated  rate,  when  it  is 
desired  that  the  steel  possess  rather  higher  tensile  strength  and 
elastic  limit  than  can  be  procured  by  very  slow  cooling.  This 
cooling  must  be  so  conducted  as  to  leave  the  steel  reasonably  free 
from  cooling  stresses.  The  manner  of  carrying  out  this  acceler- 
ated cooling  should  be  such  as  will  attain  the  desired  result. 
For  instance,  the  castings  may  be  withdrawn  from  the  furnace 
and  buried  in  a  bed  of  material  that  is  a  poor  conductor  of  heat; 


STEEL  CASTINGS 


317 


or  the  annealing  furnace  may  be  so  thrown  open  that  it  will  cool 
more  rapidly  than  it  left  closed.  Should  the  castings  be  of  such 
uneven  section  that  they  cool  at  unequal  rates  at  various  points 
when  the  furnace  is  opened,  especially  if  the  carbon  of  the  steel 
is  high,  the  furnace  should  be  closed  after  the  castings  have 
become  black,  and  their  further  cooling  so  retarded  that  the 
stresses  set  up  by  the  unequal  rates  of  cooling  are  relieved. 

Large  Steel  Castings.  —  The  work 
of  the  steel  foundry  ranges  from 
small  castings  weighing  a  few  pounds 
up  to  massive  steel  parts  weighing 
many  tons.  The  examples  shown 
in  the  accompanying  illustrations 
indicate,  in  a  general  way,  what 
has  been  accomplished  in  producing 
very  large  castings.  The  cast-steel 
rudder  frame  shown  in  Fig.  i  is 
about  22  feet  high,  28  feet  long  over 
all,  and  weighs  approximately  20 
tons.  As  the  section  is  relatively 
small  for  a  casting  of  this  size,  it 
represents  a  rather  difficult  example 
of  steel  foundry  work.  The  total 
shrinkage  in  the  height  and  length  of 
a  casting  of  this  kind  would  be  from 
2  to  3  inches;  consequently,  the  mold 
must  be  rammed  loosely  enough  so 
that  the  metal  will  crush  it  when  cooling.  If  this  did  not 
occur,  the  metal  would  either  crack  or  stretch  and  become 
weakened.  As  soon  as  the  metal  solidifies,  the  cope  should 
be  removed,  thus  uncovering  the  casting  and  assisting  in  the 
shrinkage. 

Fig.  2  shows  the  sternpost  of  a  torpedo  boat  destroyer,  the 
size  of  the  casting  being  indicated  by  the  man  standing  beside 
it.  The  large  casting  illustrated  in  Fig.  3  is  located  at  the  ex- 
treme end  of  the  bow  of  a  naval  vessel.  The  edge  at  A  is  quite 
sharp  for  cleaving  the  water  and  reducing  resistance.  The  steel 


Fig.  3.     Steel  Casting  for  the 
Bow  of  a  Ship 


IRON  AND   STEEL 


generally  used  for  locomotive  side  frames  is  an  ordinary  carbon 
steel  containing  about  0.30  per  cent  of  carbon,  but  vanadium 
steel  is  also  employed.  The  frame  illustrated  in  Fig.  4  contains 
about  0.30  per  cent  of  carbon,  and  in  molding  it,  an  indentation 
occurred  at  B  which  was  probably  caused  by  gas  or  air  being 
trapped  in  the  mold  in  the  form  of  a  bubble.  For  this  reason, 
the  casting  was  condemned  as  it  was  thought  that  there  might 

be  blow-holes  in  it.  In  order  to 
test  the  casting,  it  was  placed 
under  a  hammer  and  bent  to 
the  shape  shown  without  crack- 
ing or  even  checking  at  the 
bend.  An  unusually  large  cast- 
ing is  shown  in  Fig.  5,  which 
illustrates  a  rudder  having  a 
length  of  about  27  feet  and  a 
weight  of  22  J  tons. 

Composition  of  Steel  Cast- 
ings. -  The  composition  of 
steel  castings  recommended 
especially  for  automobile  con- 
struction, but  suitable  for  many 
other  classes  of  work,  is  as 
follows:  Carbon,  preferably 
0.35  per  cent  with  variations 
of  from  0.30  to  0.40  per  cent; 

rest  Quality  of  steel  Casting  manganese,  preferably  0.70  per 
cent  and  varying  from  0.50  to  0.80  per  cent;  silicon,  from  o.io 
to  0.30  per  cent;  phosphorus,  not  over  0.05  per  cent;  sulphur, 
not  over  0.05  per  cent.  These  specifications  have  been  adopted 
by  the  Society  of  Automotive  Engineers.  The  elastic  limit  of 
an  annealed  casting  of  this  composition  is  approximately  35,000 
pounds  per  square  inch. 

The  percentages  of  carbon,  silicon,  and  manganese  are  some- 
times varied  according  to  the  size  of  the  castings  or  their  intended 
use.  The  following  data  were  obtained  from  a  German  source: 
For  small  machine  parts,  0.50  per  cent  of  carbon,  0.25  per  cent 


Fig.  4.     Locomotive  Frame  bent  to 
T( 


STEEL  CASTINGS  319 

of  silicon,  and  0.50  per  cent  of  manganese;  for  large  machine 
parts,  from  o.io  to  0.40  per  cent  of  carbon,  from  0.20  to  0.40  per 
cent  of  silicon,  and  from  0.50  to  0.80  per  cent  of  manganese; 
castings  for  ships,  such  as  sternpost  and  rudder  frames,  from  0.20 
to  0.40  per  cent  of  carbon,  0.30  per  cent  of  silicon,  and  0.50  per 
cent  of  manganese.  Hard  castings  for  ore  crushers,  etc.,  from 
0.80  to  i. oo  per  cent  of  carbon,  from  0.20  to  0.40  per  cent  of 
silicon,  and  from  0.50  to  i.oo  per  cent  of  manganese. 

The  Union  Steel  Casting  Co.,  Pittsburg,  Pa.,  has  experimented 
considerably  with  vanadium  steel  castings.  It  has  been  found 
that  steel  castings  containing  about  0.2  per  cent  of  vanadium 
show  a  great  increase  in  tensile  strength  and  elastic  limit.  Cast- 


Fig.  5.     Cast-steel  Rudder  weighing  2 2 '/a  Tons 

ings  have  been  made  by  this  company  having  a  tensile  strength 
of  90,000  pounds  per  square  inch.  The  average  tensile  strength, 
however,  is  about  80,000  pounds  and  the  elastic  limit,  about 
45,000  pounds. 

Tests  have  indicated  that  the  quality  of  steel  castings  may 
also  be  greatly  improved  by  the  addition  of  titanium,  which  is 
said  to  improve  the  density,  strength,  toughness,  and  durability 
of  the  steel  when  properly  applied.  This  improved  quality  is 
not  the  result  of  any  direct  or  alloying  effect  of  titanium,  but  as 
the  result  of  its  value  as  a  deoxidizer  and  cleanser  in  removing 
injurious  slags  and  occluded  gases.  According  to  one  authority, 
vanadium  is  only  70  per  cent  as  efficient  as  titanium.  A  com- 
parative test  of  twenty  untreated  and  treated  steels  showed  an 
increase  in  the  ultimate  strength  of  approximately  15  per  cent, 


320  IRON   AND    STEEL 

with  no  reduction  in  elasticity  and  contraction.  An  endurance 
test  made  with  a  Wright-Souther  machine  showed  the  following 
results:  An  untreated  steel  withstood  2,676,000  revolutions  at 
a  fiber  stress  of  38,872  pounds,  whereas  titanium-treated  steel 
withstood  18,274,900  revolutions  at  pressures  varying  from 
38,872  up  to  45,939  pounds  fiber  stress.  It  is  claimed  that  the 
life  of  titanium-treated  rails  to  withstand  shocks  and  abrasion, 
and  the  life  of  gears,  is  about  50  per  cent  greater  than  when  un- 
treated steel  is  used. 

Making  Manganese  Steel  Castings.  —  In  making  manganese 
steel  castings,  the  metal  is  refined  in  a  Bessemer  converter 
from  which  it  is  poured  into  a  ladle  in  which  the  proper  quan- 
tity of  ferromanganese  has  been  previously  placed.  From  a 
metallurgical  standpoint,  there  is  nothing  to  prevent  the  suc- 
cessful production  of  manganese  steel  in  open-hearth  furnaces, 
and  it  is  possible  that  there  may  be  some  developments  in  the 
future  along  this  line,  although  at  present  the  converter  process 
is  strictly  adhered  to.  The  alloying  material  added  is  commer- 
cial 8o-per-cent  ferromanganese,  which  is  melted  in  crucibles  in 
oil-burning  furnaces.  The  quantity  of  manganese  required 
varies  somewhat  with  the  nature  of  the  castings,  but  12.5  per 
cent  is  a  good  average  figure.  To  produce  castings  that  will 
show  this  amount  of  manganese  upon  analysis,  it  is  necessary 
to  add  about  312  pounds  of  8o-per-cent  ferromanganese  to  each 
net  ton  of  steel.  After  the  steel  has  been  added  to  the  alloy,  the 
ladle  is  allowed  to  stand  for  a  few  minutes  to  permit  the  ferro- 
manganese to  remove  the  oxygen  and  other  gases  and  impuri- 
ties from  the  metal,  leaving  it  homogeneous  and  dense. 

The  shrinkage  of  the  metal  is  unusually  great,  but  otherwise 
the  principles  of  ordinary  steel  foundry  practice  apply  in  making 
the  patterns  for  manganese  kteel  castings.  The  shrinkage 
amounts  to  TSF  inch  per  foot.  Ordinary  steel  shrinks  only  about 
T\  inch.  Abrupt  changes  in  section  are  more  objectionable 
with  this  steel  than  with  other  kinds.  Manganese  steel  castings 
are  generally  allowed  to  cool  in  the  mold,  and  are  then  annealed 
for  from  3  to  26  hours  at  temperatures  ranging  from  1800  to  2000 
degrees  F.  At  the  conclusion  of  this  process,  they  are  removed 


STEEL   CASTINGS  321 

red-hot  from  the  annealing  oven  and  are  quenched  suddenly  in 
cold  water.  Some  castings,  however,  need  a  preliminary  treat- 
ment in  order  to  remove  the  cooling  strains,  and  in  this  case  they 
are  taken  from  the  sand  while  still  hot  and  slowly  cooled  in  an 
oven,  after  which  they  are  reheated  for  annealing  and  quenching, 
as  described.  Unannealed  manganese  steel  castings  are  excep- 
tionally brittle  and  almost  glass  hard.  After  the  heat- treatment, 
they  are  tough  and  ductile  with  a  tensile  strength  of  about  90,000 
pounds  and  an  elastic  limit  of  about  60,000  pounds  per  square 
inch.  After  the  castings  are  annealed,  they  are  cleaned  and 
finished  on  grinders.  Castings  which  must  be  accurately  fin- 
ished to  given  dimensions  cannot  be  machined  by  ordinary 
methods  on  account  of  their  toughness,  but  must  be  ground  to 
size. 

Semi-steel  Castings.  —  What  is  commonly  known  as  "  semi- 
steel"  and  less  frequently  as  "  toughed  cast  iron"  is  produced  .by 
adding  soft  steel  or  wrought-iron  scrap  to  the  charge  in  a  cupola. 
The  semi-steel  castings  obtained  from  this  mixture  are  cast  in 
the  same  manner  as  ordinary  castings.  The  mixture  or  charge 
for  making  semi-steel  castings  usually  contains  about  20  per 
cent  of  steel  scrap,  although  any  amount  up  to  about  70  per 
cent  may  be  used.  Semi-steel  castings  have  less  total  carbon 
than  ordinary  cast  iron,  there  seldom  being  more  than  3  per 
cent.  The  fine  grain  of  semi-steel  is  due  to  the  low  percentage 
and  fineness  of  the  graphitic  carbon.  In  producing  semi-steel, 
it  is  essential  to  secure  hot  and  uniform  melting.  A  longer  time 
is  required  to  melt  the  steel,  and  it  is  necessary  to  have  it  thor- 
oughly incorporated  with  the  iron.  It  is  common  practice  to  cast 
the  metal  into  pigs  when  first  mixing  the  steel  and  iron.  These 
pigs  are  then  remelted,  thus  insuring  a  uniformity  of  texture. 
Semi-steel  is  commonly  used  for  large  gears,  for  the  tables, 
saddles,  slides,  etc.,  of  machine  tools,  and  for  parts  requiring  a 
good  appearance. 


INDEX 


Acid  and  basic  processes,  153 
Acid  furnace,  operation,  162,  166 
Alloy  steel,  classification,  2,  4 

copper,  274 

natural,  274 

structural,  264 
Annealing  furnace,  muffle,  239 

pot,  238 

Annealing  high-speed  steel,  291 
Annealing  in  gas  medium  furnace,  236 
Annealing  steel  castings,  314 
Annealing  wire,  252 

Arc   furnaces    used  in   steel    industry, 
187 

Bars,    cold-drawn,    straightening   and 
cutting,  231 

hot-rolled,  pickling,  215 

pointed  preparatory  to  drawing,  216 

rolling,  132 
Basic  and  acid  processes,  open-hearth, 

153 

Basic  Bessemer  process,  147 
Basic  furnace  charge,  open-hearth,  172 
Basic  pig  iron,  62,  149 

classification,  4 
Beehive  oven  coke,  54 
Bertrand-Thiel  process,  179 
Bessemer   and    open-hearth   processes, 

comparison,  154 

Bessemer  converter,  operation,  139 
Bessemer  pig  iron,  62 

classification,  4 
Bessemer  process,  134 
Bessemer  steel,  8 

classification,  2,  4 

physical  characteristics,  151 
Blast  furnace  pig  iron,  34 
Blast  furnaces,  35 

fuels,  50 

flux,  58 
Blast  stoves,  42 


Blister  steel,  classification,  4 
Brinell  test  for  steel,  93,  94 
Briquetting  of  ore,  32 
Brown  hematite  ore,  19 
By-product  coke  ovens,  55 
By-products,  recovery,  57 

Carbonate  iron  ore,  20 

Carbon  content  of  steel,  determining,  122 

Carbon,  influence  of,  on  cast  iron,  302 

influence  of,  on  high-speed  steels,  283 

influence  of,  on  steel,  no 
Carbon  steel,  for  screw  machine  work, 
260 

structural,  254 

structural,  properties  and  uses,  259 
Carbon- temper  of  steel,  132 
Casehardened  steel,  microscopic  study, 

101 
Casehardening,  255 

for  colors,  258 
Castings,  chilled,  306 

growth  of,  304 

iron,  production,  299 

malleable,  classification,  4 

malleable  iron,  308 

manganese  steel,  method  of  making. 
320 

methods  of  hardening,  304 

semi-steel,  321 

steel,  9 

steel,  annealing,  314 

steel,  composition,  318 

steel,  materials,  311 

steel,  processes  for  making,  312 

steel,  strength  of,  310 
Cast  iron,  9,  298 

alloying  elements,  303 

classification,  2,  4,  5 

influence  of  carbon,  302 

influence  of  silicon,  302 

mixtures  for  different  grades,  300 


323 


3  24 


INDEX 


Cast  iron,  seasoning,  305 

strength,  303 

Cast  steel,  classification,  4 
Cementation  process,  117 
Charcoal   hearth    cast   iron,    classifica- 
tion, 4 

Charging  machines,  166 
Chilled  castings,  306 
Chrome- vanadium  steel,  270 
Chromium,  influence  of,  on  steel,  286 
Chromium  steel,  265 
Coal,  coking,  54 
Coke,  51,  54 

Coke  ovens,  by-product,  55 
Coking  coals,  54 
Coking  process,  53 

Cold-drawing  process,  advantages,  226 
Cold-drawn    bars,     straightening    and 

cutting,  231 

Cold-drawn  shafting,  214 
CoM-rolled  steel,  polishing,  247 
Cold-rolling  operation,  241 
Cold-rolling  strip  steel,  234 
Converted  steel,  classification,  4 
Converters,  Bessemer,  137 

effect    of   raw    material   on    action, 
141 

operation  of,  139 
Copper  alloy  steel,  274 
Copper,  effect  of,  on  steel,  115 
Crucible  furnace,  operating,  126 
Crucible  process,  118 
Crucibles,  charging,  121 

for  making  crucible  steel,  118 
Crucible  steel,  8,  117 

classification,  2,  4 

grades,  133 

Dies,  drawing,  lubricants,  230 

for  drawing  irregular  shapes,  229 

for  drawing  rectangles,  229 

for  drawing  shafting  and  screw  stock, 
227 

for  drawing  small  stock,  226 

for  drawing  squares,  229 
Draw-bench,  rotary  type,  222 

types  of,  220 
Drawing  dies,  lubricants,  230 


Drawplates,  251 
Duplex  process,  179 

Electric    furnaces,    application    of,    in 
steel  industry,  181,  314 

Booth-Hall,  194 

current  consumption,  202 

electrodes,  200 

general  classes,  183 

Girod,  199 

Greaves-Etchells,  198 

Heroult,  188 

linings,  202 

Ludlum,  196 

operating,  185 

Rennerfelt,  192 

Snyder,  190 

Electric  process,  advantages,  186 
Electric  steel,  181 

Electrodes  for  electric  furnaces,  200 
Etching  reagents  for  hardened  steel,  108 

Ferrosilicon  pig  iron,  63 
Flux  used  in  blast  furnace,  58 
Foundry  pig  iron,  61 
Franklinite,  21 
Fuels  for  blast  furnaces,  50 
Furnaces,  blast,  35 

blast,  fuels,  50 

blast,  flux,  58 

charging,  44 

crucible,  operating,  126 

electric,  application  of,  in  steel  in- 
dustry, 181,  314 

electric,  Booth-Hall,  194 

electric,  current  consumption,  202 

electric,  electrodes,  200 

electric,  Girod,  199 

electric,  Greaves-Etchells,  198 

electric,  Heroult,  188 

electric,  linings,  202 

electric,  Ludlum,  196 

electric,  operating,  185 

electric,  Rennerfelt,  192 

electric,  Snyder,  190 

gas-fired  regenerative,  124 

gas  medium,  annealing,  236 

Krupp  regenerative,  125 


INDEX 


325 


Furnaces,  muffle  annealing,  239 
oil-burning,  124 
open-hearth,  154 
pot-annealing,  238 
tilting,  176 

Gages,  wire,  253 

Gas-fired  regenerative  furnaces,  124 

Gas  medium  furnace,  annealing,  236 

Gas,  producer,  162 

Goethite,  20 

Graphite  crucibles,  121 

Gray  cast  iron,  classification,  4 

Gray  forge  iron,  63 

Gray  pig  iron,  classification,  4 

Hardening  and  tempering,  246 
Hardening  castings,  methods,  304 
Hardening  high-speed  steel  290 
Hardness  of  steel,  determining,  92 
Heat-treated  steel,  microscopic  study, 

99 

Heat-treatment,  effect  of,  on  durabil- 
ity, 278 

of  tools  with  fine  edges.  294 

Taylor-White  method,  279 
Hematite  ore,  18,  19 
High-speed  steel,  276 

annealing,  291 

cutting  ends  on  tools,  295 

effect  of  carbon,  283 

effect  of  different  elements,  282 

hardening,  290 

production,  280 

tempering,  291 

tungstenless,  288 

uranium,  288 

uses,  296 
Hot-rolled  bars,  pickling,  215 

Ilmenite,  21 

Ingot  molds,  127 

Ingots,  method  of  making,  171 

pouring,  143 
Iron,  alloy  cast,  classification,  3 

basic  pig,  62,  149 

basic  pig,  classification,  4 


Iron,  Bessemer  pig,  62 
cast,  9,  298 

cast,  classification,  2,  4 
cast,  mixtures  for  different  grades,  300 
cast,  seasoning,  305 
cast,  strength,  303 
common  wrought,  made  from  pig  iron, 

70 

common  wrought,  made  from  scrap ,  72 
ferrosilicon  pig,  63 
foundry  pig,  61 
gray  cast,  classification,  4 
gray  pig,  classification,  4 
malleable,  classification,  4 
malleable  pig,  classification,  4 
open-hearth,  79 

pig,  34 

pig,  classification,  2,  5 

pig,  grading,  61,  64 

pig,  influence  of  various  elements,  59 

pig,  mottled  and  white,  63 

pig,  produced  in  blast  furnace,  34 

puddled,  classification,  5 

pure,  i 

refined  cast,  classification,  5 

Scotch  pig,  63 

weld,  classification,  5 

white  cast,  classification,  5 

wrought,  7,  65 

wrought,  and  low-carbon  steel,  differ- 
ences, 78 

wrought,  classification,  2,  5,  67 

wrought,  corrosion,  68 

wrought,  defects,  75 

wrought,  manufacture,  69 

wrought,  specifications,  77 

wrought,  strength,  66 

wrought,  testing,  75,  76 

Yorkshire  wrought,  74 
Iron  and  steel,  classification,  i,  3 

commercial,  2 

strength,  13 

Iron-  and  steel-making  processes,  5 
Iron  castings,  malleable,  308 

production,  299 
Iron  industry,  history,  9 
Iron  ore,  beneficiation,  27 

commercial,  16 


326 


INDEX 


Iron  ore,  commercial,  richness  of,  24 
deposits,  24 

factors  determining  value,  21 
hand  picking  or  cobbing,  28 
influence  of  various  elements,  23 
jigging,  29 
mining,  26 

preparation  for  smelting,  16 
roasting,  29 
washing,  29 

Keep  drill  test,  for  steel,  93,  94 
Krupp  regenerative  ftirnaces,  125 

Lancashire  process,  75 

Limonite,  19 

Low-carbon    steel    and    wrought   iron, 

differences,  78 
Lubricants  used  on  drawing  dies,  230 

Magnetic  concentration  of  ore,  31 
Magnetic-mechanical   analysis,  perme- 

ameter,  108 
Magnetic  oxide  produced  from  iron  ore, 

30 

Magnetite  ore,  17 
Malleable  iron  castings,  4,  308 
Malleable  pig  iron,  classification,  4 
Manganese,  influence  of,  on  pig  iron,  59 

influence  of,  on  steel,  112,  284 
Manganese  steel,  265 
Manganese   steel   castings,   method   of 

making,  320 
Manganese,  sulphur,  and  phosphorus, 

influence  of,  302 
Metal,  recarburizing,  168 
Metal,  testing,  169 
Microscopic    study    of    casehardened 

steel,  lor 

Microscopic  study  of  steel,  94,  99 
Mixers,  149 
Molds,  ingot,  127 
Molybdenum,    influence   of,    on    steel, 

287 

Monell  process,  179 
Mottled  and  white  pig  iron,  63 
Muffle  annealing  furnace,  239 
Mushet  steel,  277 


Natural  alloy  steel,  274 
Natural  gas,  161 
Nickel-chromium  steel,  272 
Nickel  steel,  267 
Nodulizing  of  ore,  32 

Oil  as  fuel,  161 
Oil-burning  furnaces,  124 
Open-hearth  and   Bessemer  processes, 

comparison,  154 
Open-hearth  furnaces,  154 
Open-hearth  iron,  79 
Open-hearth  process,  description,  152 

tonnage  produced,  134 
Open-hearth  steel,  8,  152 

classification,  2,  5 

physical  characteristics,  180 
Ore,  agglomeration,  32 

briquetting,  32 

carbonate  iron,  20 

commercial  iron,  richness  of,  24 

iron,  beneficiation  of,  27 

iron,  commercial,  16 

iron,  deposits,  24 

iron,  factors  determining  value,  21 

iron,  influence  of  various  elements,  23 

iron,  jigging,  29 

iron,  preparation  for  smelting,  16 

iron,  roasting,  29 

iron,  washing,  29 

magnetic  concentration,  31 

magnetite,  17 

nodulizing,  32 

oolitic,  20 

red  hematite,  18 

sintering,  33 

transformed  into  magnetic  oxide,  30 
Ovens,  beehive,  for  producing  coke,  54 

by-product  coke,  55 

Permeameter  for  magnetic-mechanical 

analysis,  108 

Phosphorus  and  sulphur,  elimination,  1 74 
Phosphorus,  influence  of,  on  iron  ore,  23 
influence  of,  on  pig  iron,  60 
influence  of,  on  steel,  112 
sulphur,  and  manganese,  influence  of, 
302 


INDEX 


327 


Photo-micrographs  of  iron  and   steel, 

103 

Pickling  hot-rolled  bars,  215 
Pickling  stock  before  cold  rolling,  240 
Pig-casting  machines,  47 
Pig  iron,  basic,  4,  62,  149 

Bessemer,  4,  62 

classification,  2,  5 

ferrosilicon,  63 

foundry,  61 

grading,  61,  64 

influence  of  various  elements,  59 

made  into  common  wrought  iron,  70 

malleable,  classification,  4 

mottled  and  white,  63 

produced  in  blast  furnace,  34 

Scotch,  63 
Piping,  129,  145 
Pot  annealing  furnace,  238 
Producer  gas,  162 
Puddled  iron,  classification,  5 
Puddled  steel,  classification,  5 
Pyrite,  21 

Ram's-horn  test,  76 
Recarburizers,  adding,  175 
Recarburizing  metal,  142,  168 
Recarburizing  methods,  143 
Refined  cast  iron,  classification,  5 
Regenerative  furnaces,  gas-fired,  124 
Regenerators,  160 
Rolling  mill,  205 
Rolling  process,  208 
Rolling  wire  rod,  212 
Roof  of  open-hearth  furnace,  158 
Rotary  type  draw-bench,  222 

Sclerometer  test  for  steel,  92 
Scleroscope  test  for  steel,  93,  94 
Scrap  made  into  common  wrought  iron, 

72 

Segregation,  145 
Self-hardening  steel,  origin,  277 
Semi-high-speed  steel,  288 
Semi-steel  castings,  321 
Shafting,  cold-drawn,  214 

dies  for  drawing,  227 
Shear  steel,  classification,  5 


Silicon,  influence  of,  on  cast  iron,  302 

influence  of,  on  pig  iron,  60 

influence  of,  on  steel,  115,  287 
Sintering  of  ore,  33 
Slag,  48 

basic-hearth,  176 

commercial  uses,  50 

utilization,  149 
Soaking  pits,  146 
Spark  test  for  steel,  90 
Speeds  for  cold-drawing,  224 
Spiegeleisen,  63 
Spring  steel,  262 
Steel,  alloy,  classification,  2,  4 

Bessemer,  8,  134,  151 

Bessemer,  classification,  2,  4 

blister,  classification,  4 

carbon,  259 

carbon-temper,  132 

casehardened,  microscopic  study,  101 

cast,  classification,  4 

characteristics  and  classification,  81,82 

chrome- vanadium,  270 

chromium,  265 

classification,  5 

constituents  revealed  by  microscope, 

97 

copper  alloy,  274 

crucible,  8,  117 

crucible,  grades,  133 

determining  carbon  content,  122 

distinguished  from  wrought  iron,  80 

effect  of  different  elements,  no 

effect  of  method  of  working  on 
strength,  87 

electric,  181 

for  cold-drawn  shafting,  214 

heat-treated,  microscopic  study,  99 

high-speed,  276 

high-speed,  annealing,  291 

high-speed,  effect  of  different  ele- 
ments, 282 

high-speed,  hardening,  290 

high-speed,  production,  280 

high-speed,  uses,  296 

influence  of  various  metals  on  cor- 
rosiveness,  115 

Keep  drill  test,  93,  94 


328 


INDEX 


Steel,   low-carbon,   and   wrought    iron, 
differences,  78 

manganese,  265 

microscopic  study,  94 

mushet,  277 

natural  alloy,  274 

nickel,  267 

nickel-chromium,  272 

open-hearth,  8,  152 

open-hearth,  classification,  2,  5 

open-hearth,  physical  characteristics, 
1 80 

puddled,  classification,  5 

self -hardening,  origin,  277 

semi-high-speed,  288 

shear,  classification,  5 

spring,  262 

structural  alloy,  264 

structural  carbon,  254 

titanium,  269 

tungstenless  high-speed,  288 

uranium  high-speed,  288 

vanadium,  270 
Steel  and  iron,  classification,  i,  3 

commercial,  2 

photo-micrographs,  103 

strength,  13 

Steel-  and  iron-making,  processes,  5 
Steel  castings,  9,  310 

annealing,  314 

classification,  2,  5 

composition,  318 

large  size,  317 

manganese,  method  of  making,  320 

materials,  311 

processes  for  making,  312 

strength,  310 
Steel  foundry,  using  electric    furnace, 

3H 

Stoves,  blast,  42 
Strip  steel,  cold-rolling,  234 
Structural  alloy  steels,  264 
Structural  carbon  steel,  254 
Sulphur  and  phosphorus,  elimination, 

i74 

Sulphur,  influence  of,  on  iron  ore,  23 
influence  of,  on  pig  iron,  60 
influence  of,  on  steel,  113 


Talbot  continuous  process,  177 

Taylor-White  method  of  heat-treat- 
ment, 279 

Tempering  and  hardening,  246 

Tempering  high-speed  steel,  291 

Tilting  furnaces,  176 

Titanium  steel,  269 

Tonnage  produced  by  Bessemer  and 
open-hearth  processes,  134 

Tools  with  high-speed  steel  cutting 
ends,  295 

Tungsten,  influence  of,  on  steel,  284 

Tungstenless  high-speed  steel,  288 

Turgite,  19 

Tuyeres,  40 

Uranium  high-speed  steel,  288 

Vanadium,  influence  of,  on  steel,  287 
Vanadium  steel,  270 

\Valloon  process,  74 
Washed  metal,  classification,  5 
Weld  iron,  classification,  5 
White  cast  iron,  classification,  5 
White  pig  iron,  classification,  5 
Wire,  annealing,  252 
Wire  drawing,  249 
Wire  gages,  253 
Wire  rod  rolling,  212 
Wrought  iron,  7,  65 

and  low-carbon  steel,  differences,  78 

characteristics,  65 

classification,  2,  5,  67 

common,  made  from  pig  iron,  70 

common,  made  from  scrap,  72 

corrosion,  68 

defects,  75 

distinguished  from  steel,  80 

manufacture,  69 

processes,  73 

ram's-horn  test,  76 

specifications,  77 

strength,  66 

testing,  75 

Yorkshire,  74 
Wrought-iron  chain,  77 

Yorkshire  wrought  iron,  74 


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